Fixes #3787 -- ESLint updates and linting cleanup (#3790)

* ESLint updates and linting cleanup * Exclude test files from some linting rules for now * Fix some TypeScript and build issues
2026-01-08 23:28:04 -05:00 · 2023-04-08 09:27:41 -07:00
parent a917965340
commit 4d3189c051
68 changed files with 449 additions and 442 deletions
--- a/packages/less/.eslintrc.js
+++ b/packages/less/.eslintrc.js
@@ -0,0 +1,63 @@
+module.exports = {
+    'parser': '@typescript-eslint/parser',
+    'extends': 'eslint:recommended',
+    'parserOptions': {
+        'ecmaVersion': 2018,
+        'sourceType': 'module'
+    },
+    'plugins': ['@typescript-eslint'],
+    'env': {
+        'browser': true,
+        'node': true,
+        'mocha': true
+    },
+    'globals': {},
+    'rules': {
+        indent: ['error', 4, {
+            SwitchCase: 1
+        }],
+        'no-empty': ['error', { 'allowEmptyCatch': true }],
+        quotes: ['error', 'single', {
+            avoidEscape: true
+        }],
+        /**
+         * The codebase uses some while(true) statements.
+         * Refactor to remove this rule.
+         */
+        'no-constant-condition': 0,
+        /**
+         * Less combines assignments with conditionals sometimes
+         */
+        'no-cond-assign': 0,
+        /**
+         * @todo - remove when some kind of code style (XO?) is added
+         */
+        'no-multiple-empty-lines': 'error'
+    },
+    'overrides': [
+        {
+            files: ['*.ts'],
+            extends: ['plugin:@typescript-eslint/recommended'],
+            rules: {
+                /**
+                 * Suppress until Less has better-defined types
+                 * @see https://github.com/less/less.js/discussions/3786
+                 */
+                '@typescript-eslint/no-explicit-any': 0
+            }
+        },
+        {
+            files: ['test/**/*.{js,ts}', 'benchmark/index.js'],
+            /**
+             * @todo - fix later
+             */
+            rules: {
+                'no-undef': 0,
+                'no-useless-escape': 0,
+                'no-unused-vars': 0,
+                'no-redeclare': 0,
+                '@typescript-eslint/no-unused-vars': 0
+            }
+        },
+    ]
+}
--- a/packages/less/.eslintrc.json
+++ b/packages/less/.eslintrc.json
@@ -1,71 +0,0 @@
-{
-    "parser": "@typescript-eslint/parser",
-    "parserOptions": {
-        "ecmaVersion": 2018,
-        "sourceType": "module"
-    },
-    "plugins": ["@typescript-eslint"],
-    "env": {
-        "browser": true,
-        "node": true
-    },
-    "globals": {},
-    "rules": {
-        "no-eval": 2,
-        "no-use-before-define": [
-            2,
-            {
-                "functions": false
-            }
-        ],
-        "no-undef": 0,
-        "no-unused-vars": 1,
-        "no-caller": 2,
-        "no-eq-null": 1,
-        "guard-for-in": 2,
-        "no-implicit-coercion": [
-            2,
-            {
-                "boolean": false,
-                "string": true,
-                "number": true
-            }
-        ],
-        "no-with": 2,
-        "no-mixed-spaces-and-tabs": 2,
-        "no-multiple-empty-lines": 2,
-        "dot-location": [2, "property"],
-        "operator-linebreak": [0, "after"],
-        "keyword-spacing": [2, {}],
-        "space-unary-ops": [
-            2,
-            {
-                "words": false,
-                "nonwords": false
-            }
-        ],
-        "no-spaced-func": 2,
-        "space-before-function-paren": [
-            1,
-            {
-                "anonymous": "ignore",
-                "named": "never"
-            }
-        ],
-        "comma-dangle": [2, "never"],
-        "no-trailing-spaces": 0,
-        "max-len": [2, 160],
-        "comma-style": [2, "last"],
-        "curly": [2, "all"],
-        "space-infix-ops": 2,
-        "spaced-comment": 1,
-        "space-before-blocks": [2, "always"],
-        "indent": [
-            2,
-            4,
-            {
-                "SwitchCase": 1
-            }
-        ]
-    }
-}
--- a/packages/less/Gruntfile.js
+++ b/packages/less/Gruntfile.js
@@ -283,7 +283,7 @@ module.exports = function(grunt) {
                "!test/less/errors/plugin/plugin-error.js"
            ],
            options: {
-                configFile: ".eslintrc.json",
+                configFile: ".eslintrc.js",
                fix: true
            }
        },
--- a/packages/less/benchmark/index.js
+++ b/packages/less/benchmark/index.js
@@ -1,6 +1,6 @@
 var path = require('path'),
    fs = require('fs'),
-    now = require("performance-now");
+    now = require('performance-now');

 var less = require('../.');
 var file = path.join(__dirname, 'benchmark.less');
@@ -10,12 +10,12 @@ if (process.argv[2]) { file = path.join(process.cwd(), process.argv[2]) }
 fs.readFile(file, 'utf8', function (e, data) {
    var start, total;

-    console.log("Benchmarking...\n", path.basename(file) + " (" +
-             parseInt(data.length / 1024) + " KB)", "");
+    console.log('Benchmarking...\n', path.basename(file) + ' (' +
+             parseInt(data.length / 1024) + ' KB)', '');

    var renderBenchmark = []
-      , parserBenchmark = []
-      , evalBenchmark = [];
+        , parserBenchmark = []
+        , evalBenchmark = [];

    var totalruns = 30;
    var ignoreruns = 5;
@@ -74,13 +74,13 @@ fs.readFile(file, 'utf8', function (e, data) {
            var variation = maxtime - mintime;
            var variationperc = (variation / avgtime) * 100;

-            console.log("Min. Time: " + Math.round(mintime) + " ms");
-            console.log("Max. Time: " + Math.round(maxtime) + " ms");
-            console.log("Total Average Time: " + Math.round(avgtime) + " ms (" +
+            console.log('Min. Time: ' + Math.round(mintime) + ' ms');
+            console.log('Max. Time: ' + Math.round(maxtime) + ' ms');
+            console.log('Total Average Time: ' + Math.round(avgtime) + ' ms (' +
                parseInt(1000 / avgtime *
-                data.length / 1024) + " KB\/s)");
-            console.log("+/- " + Math.round(variationperc) + "%");
-            console.log("");
+                data.length / 1024) + ' KB\/s)');
+            console.log('+/- ' + Math.round(variationperc) + '%');
+            console.log('');
        }
       
        analyze('Parsing', parserBenchmark);
--- a/packages/less/build/rollup.js
+++ b/packages/less/build/rollup.js
@@ -47,7 +47,7 @@ async function buildBrowser() {
                include: [/^.+\.min\.js$/],
                output: {
                    comments: function(node, comment) {
-                        if (comment.type == "comment2") {
+                        if (comment.type == 'comment2') {
                            // preserve banner
                            return /@license/i.test(comment.value);
                        }
--- a/packages/less/package.json
+++ b/packages/less/package.json
@@ -37,11 +37,13 @@
 	"scripts": {
 		"test": "grunt test",
 		"grunt": "grunt",
+		"lint": "eslint '**/*.{ts,js}'",
+		"lint:fix": "eslint '**/*.{ts,js}' --fix",
 		"build": "npm-run-all clean compile",
 		"clean": "shx rm -rf ./lib tsconfig.tsbuildinfo",
-		"compile": "tsc -p tsconfig.json",
+		"compile": "tsc -p tsconfig.build.json",
 		"copy:root": "shx cp -rf ./dist ../../",
-		"dev": "tsc -p tsconfig.json -w",
+		"dev": "tsc -p tsconfig.build.json -w",
 		"prepublishOnly": "grunt dist"
 	},
 	"optionalDependencies": {
--- a/packages/less/src/less-browser/bootstrap.js
+++ b/packages/less/src/less-browser/bootstrap.js
@@ -3,8 +3,6 @@
 * used in the browser distributed version of less
 * to kick-start less using the browser api
 */
-/* global window, document */
-
 import defaultOptions from '../less/default-options';
 import addDefaultOptions from './add-default-options';
 import root from './index';
@@ -13,7 +11,7 @@ const options = defaultOptions();

 if (window.less) {
    for (const key in window.less) {
-        if (window.less.hasOwnProperty(key)) {
+        if (Object.prototype.hasOwnProperty.call(window.less, key)) {
            options[key] = window.less[key];
        }
    }
--- a/packages/less/src/less-browser/cache.js
+++ b/packages/less/src/less-browser/cache.js
@@ -29,7 +29,7 @@ export default (window, options, logger) => {
            let vars      = cache && cache.getItem(`${path}:vars`);

            modifyVars = modifyVars || {};
-            vars = vars || "{}"; // if not set, treat as the JSON representation of an empty object
+            vars = vars || '{}'; // if not set, treat as the JSON representation of an empty object

            if (timestamp && webInfo.lastModified &&
                (new Date(webInfo.lastModified).valueOf() ===
--- a/packages/less/src/less-browser/error-reporting.js
+++ b/packages/less/src/less-browser/error-reporting.js
@@ -11,7 +11,7 @@ export default (window, less, options) => {
        let content;
        const errors = [];
        const filename = e.filename || rootHref;
-        const filenameNoPath = filename.match(/([^\/]+(\?.*)?)$/)[1];
+        const filenameNoPath = filename.match(/([^/]+(\?.*)?)$/)[1];

        elem.id        = id;
        elem.className = 'less-error-message';
@@ -113,7 +113,7 @@ export default (window, less, options) => {
        }
    }

-    function removeErrorConsole(path) {
+    function removeErrorConsole() {
        // no action
    }

--- a/packages/less/src/less-browser/file-manager.js
+++ b/packages/less/src/less-browser/file-manager.js
@@ -1,5 +1,3 @@
-/* global window, XMLHttpRequest */
-
 import AbstractFileManager from '../less/environment/abstract-file-manager.js';

 let options;
@@ -66,7 +64,7 @@ FileManager.prototype = Object.assign(new AbstractFileManager(), {
        fileCache = {};
    },

-    loadFile(filename, currentDirectory, options, environment) {
+    loadFile(filename, currentDirectory, options) {
        // TODO: Add prefix support like less-node?
        // What about multiple paths?

--- a/packages/less/src/less-browser/index.js
+++ b/packages/less/src/less-browser/index.js
@@ -39,7 +39,7 @@ export default (window, options) => {
    function clone(obj) {
        const cloned = {};
        for (const prop in obj) {
-            if (obj.hasOwnProperty(prop)) {
+            if (Object.prototype.hasOwnProperty.call(obj, prop)) {
                cloned[prop] = obj[prop];
            }
        }
@@ -159,6 +159,10 @@ export default (window, options) => {
            less.watchTimer = setInterval(() => {
                if (less.watchMode) {
                    fileManager.clearFileCache();
+                    /**
+                     * @todo remove when this is typed with JSDoc
+                     */
+                    // eslint-disable-next-line no-unused-vars
                    loadStyleSheets((e, css, _, sheet, webInfo) => {
                        if (e) {
                            errors.add(e, e.href || sheet.href);
@@ -174,7 +178,7 @@ export default (window, options) => {
    //
    // Watch mode
    //
-    less.watch   = function () {
+    less.watch = function () {
        if (!less.watchMode ) {
            less.env = 'development';
            initRunningMode();
@@ -205,7 +209,7 @@ export default (window, options) => {
    // Asynchronously get all <link> tags with the 'rel' attribute set to
    // "stylesheet/less", returning a Promise.
    //
-    less.registerStylesheets = () => new Promise((resolve, reject) => {
+    less.registerStylesheets = () => new Promise((resolve) => {
        less.registerStylesheetsImmediately();
        resolve();
    });
--- a/packages/less/src/less-browser/plugin-loader.js
+++ b/packages/less/src/less-browser/plugin-loader.js
@@ -1,6 +1,6 @@
-// TODO: Add tests for browser @plugin
-/* global window */
-
+/**
+ * @todo Add tests for browser `@plugin`
+ */
 import AbstractPluginLoader from '../less/environment/abstract-plugin-loader.js';

 /**
--- a/packages/less/src/less-browser/utils.js
+++ b/packages/less/src/less-browser/utils.js
@@ -1,17 +1,17 @@

 export function extractId(href) {
-    return href.replace(/^[a-z-]+:\/+?[^\/]+/, '')  // Remove protocol & domain
-        .replace(/[\?\&]livereload=\w+/, '')        // Remove LiveReload cachebuster
+    return href.replace(/^[a-z-]+:\/+?[^/]+/, '')  // Remove protocol & domain
+        .replace(/[?&]livereload=\w+/, '')        // Remove LiveReload cachebuster
        .replace(/^\//, '')                         // Remove root /
        .replace(/\.[a-zA-Z]+$/, '')                // Remove simple extension
-        .replace(/[^\.\w-]+/g, '-')                 // Replace illegal characters
+        .replace(/[^.\w-]+/g, '-')                 // Replace illegal characters
        .replace(/\./g, ':');                       // Replace dots with colons(for valid id)
 }

 export function addDataAttr(options, tag) {
    if (!tag) {return;} // in case of tag is null or undefined
    for (const opt in tag.dataset) {
-        if (tag.dataset.hasOwnProperty(opt)) {
+        if (Object.prototype.hasOwnProperty.call(tag.dataset, opt)) {
            if (opt === 'env' || opt === 'dumpLineNumbers' || opt === 'rootpath' || opt === 'errorReporting') {
                options[opt] = tag.dataset[opt];
            } else {
--- a/packages/less/src/less-node/file-manager.js
+++ b/packages/less/src/less-node/file-manager.js
@@ -61,6 +61,23 @@ FileManager.prototype = Object.assign(new AbstractFileManager(), {

        function getFileData(fulfill, reject) {
            (function tryPathIndex(i) {
+                function tryWithExtension() {
+                    const extFilename = options.ext ? self.tryAppendExtension(fullFilename, options.ext) : fullFilename;
+
+                    if (extFilename !== fullFilename && !explicit && paths[i] === '.') {
+                        try {
+                            fullFilename = require.resolve(extFilename);
+                            isNodeModule = true;
+                        }
+                        catch (e) {
+                            filenamesTried.push(npmPrefix + extFilename);
+                            fullFilename = extFilename;
+                        }
+                    }
+                    else {
+                        fullFilename = extFilename;
+                    }
+                }
                if (i < paths.length) {
                    (function tryPrefix(j) {
                        if (j < prefixes.length) {
@@ -83,25 +100,7 @@ FileManager.prototype = Object.assign(new AbstractFileManager(), {
                            }
                            else {
                                tryWithExtension();
-                            }
-
-                            function tryWithExtension() {
-                                const extFilename = options.ext ? self.tryAppendExtension(fullFilename, options.ext) : fullFilename;
-
-                                if (extFilename !== fullFilename && !explicit && paths[i] === '.') {
-                                    try {
-                                        fullFilename = require.resolve(extFilename);
-                                        isNodeModule = true;
-                                    }
-                                    catch (e) {
-                                        filenamesTried.push(npmPrefix + extFilename);
-                                        fullFilename = extFilename;
-                                    }
-                                }
-                                else {
-                                    fullFilename = extFilename;
-                                }
-                            }
+                            }                            

                            const readFileArgs = [fullFilename];
                            if (!options.rawBuffer) {
--- a/packages/less/src/less-node/lessc-helper.js
+++ b/packages/less/src/less-node/lessc-helper.js
@@ -88,4 +88,5 @@ const lessc_helper = {
 };

 // Exports helper functions
+// eslint-disable-next-line no-prototype-builtins
 for (const h in lessc_helper) { if (lessc_helper.hasOwnProperty(h)) { exports[h] = lessc_helper[h]; }}
--- a/packages/less/src/less-node/url-file-manager.js
+++ b/packages/less/src/less-node/url-file-manager.js
@@ -1,3 +1,8 @@
+/* eslint-disable no-unused-vars */
+/**
+ * @todo - remove top eslint rule when FileManagers have JSDoc type
+ * and are TS-type-checked
+ */
 const isUrlRe = /^(?:https?:)?\/\//i;
 import url from 'url';
 let request;
--- a/packages/less/src/less/contexts.js
+++ b/packages/less/src/less/contexts.js
@@ -6,7 +6,7 @@ const copyFromOriginal = function copyFromOriginal(original, destination, proper
    if (!original) { return; }

    for (let i = 0; i < propertiesToCopy.length; i++) {
-        if (original.hasOwnProperty(propertiesToCopy[i])) {
+        if (Object.prototype.hasOwnProperty.call(original, propertiesToCopy[i])) {
            destination[propertiesToCopy[i]] = original[propertiesToCopy[i]];
        }
    }
@@ -113,7 +113,7 @@ contexts.Eval.prototype.pathRequiresRewrite = function (path) {
 contexts.Eval.prototype.rewritePath = function (path, rootpath) {
    let newPath;

-    rootpath = rootpath || '';
+    rootpath = rootpath || '';
    newPath = this.normalizePath(rootpath + path);

    // If a path was explicit relative and the rootpath was not an absolute path
--- a/packages/less/src/less/default-options.js
+++ b/packages/less/src/less/default-options.js
@@ -67,4 +67,4 @@ export default function() {
        /* This option allows you to specify a argument to go on to every URL.  */
        urlArgs: ''
    }
-};
+}
--- a/packages/less/src/less/environment/abstract-file-manager.js
+++ b/packages/less/src/less/environment/abstract-file-manager.js
@@ -15,7 +15,7 @@ class AbstractFileManager {
    }

    tryAppendExtension(path, ext) {
-        return /(\.[a-z]*$)|([\?;].*)$/.test(path) ? path : path + ext;
+        return /(\.[a-z]*$)|([?;].*)$/.test(path) ? path : path + ext;
    }

    tryAppendLessExtension(path) {
@@ -71,7 +71,13 @@ class AbstractFileManager {
        return diff;
    }

-    // helper function, not part of API
+    /**
+     * Helper function, not part of API.
+     * This should be replaceable by newer Node / Browser APIs
+     * 
+     * @param {string} url 
+     * @param {string} baseUrl
+     */
    extractUrlParts(url, baseUrl) {
        // urlParts[1] = protocol://hostname/ OR /
        // urlParts[2] = / if path relative to host base
@@ -79,7 +85,7 @@ class AbstractFileManager {
        // urlParts[4] = filename
        // urlParts[5] = parameters

-        const urlPartsRegex = /^((?:[a-z-]+:)?\/{2}(?:[^\/\?#]*\/)|([\/\\]))?((?:[^\/\\\?#]*[\/\\])*)([^\/\\\?#]*)([#\?].*)?$/i;
+        const urlPartsRegex = /^((?:[a-z-]+:)?\/{2}(?:[^/?#]*\/)|([/\\]))?((?:[^/\\?#]*[/\\])*)([^/\\?#]*)([#?].*)?$/i;

        const urlParts = url.match(urlPartsRegex);
        const returner = {};
--- a/packages/less/src/less/environment/environment-api.js
+++ b/packages/less/src/less/environment/environment-api.js
@@ -1,25 +0,0 @@
-export default {
-    /**
-     * Converts a string to a base 64 string
-     * @param str
-     */
-    encodeBase64: function(str) {
-    },
-    /**
-     * Lookup the mime-type of a filename
-     * @param filename
-     */
-    mimeLookup: function (filename) {
-    },
-    /**
-     * Look up the charset of a mime type
-     * @param mime
-     */
-    charsetLookup: function (mime) {
-    },
-    /**
-     * Gets a source map generator
-     */
-    getSourceMapGenerator: function getSourceMapGenerator() {
-    }
-};
--- a/packages/less/src/less/environment/environment-api.ts
+++ b/packages/less/src/less/environment/environment-api.ts
@@ -0,0 +1,21 @@
+export interface Environment {
+    /**
+     * Converts a string to a base 64 string
+     */
+    encodeBase64(str: string): string
+    /**
+     * Lookup the mime-type of a filename
+     */
+    mimeLookup(filename: string): string
+    /**
+     * Look up the charset of a mime type
+     * @param mime
+     */
+    charsetLookup(mime: string): string
+    /**
+     * Gets a source map generator
+     *
+     * @todo - Figure out precise type
+     */
+    getSourceMapGenerator(): any
+}
--- a/packages/less/src/less/environment/file-manager-api.js
+++ b/packages/less/src/less/environment/file-manager-api.js
@@ -1,103 +0,0 @@
-export default {
-    /**
-     * Given the full path to a file, return the path component
-     * Provided by AbstractFileManager
-     * @param {string} filename
-     * @returns {string}
-     */
-    getPath: function(filename) {
-    },
-    /**
-     * Append a .less extension if appropriate. Only called if less thinks one could be added.
-     * Provided by AbstractFileManager
-     * @param filename
-     * @returns {string}
-     */
-    tryAppendLessExtension: function(filename) {
-    },
-    /**
-     * Whether the rootpath should be converted to be absolute.
-     * The browser ovverides this to return true because urls must be absolute.
-     * Provided by AbstractFileManager (returns false)
-     * @returns {bool}
-     */
-    alwaysMakePathsAbsolute: function() {
-    },
-    /**
-     * Returns whether a path is absolute
-     * Provided by AbstractFileManager
-     * @param {string} path
-     * @returns {bool}
-     */
-    isPathAbsolute: function(path) {
-    },
-    /**
-     * joins together 2 paths
-     * Provided by AbstractFileManager
-     * @param {string} basePath
-     * @param {string} laterPath
-     */
-    join: function(basePath, laterPath) {
-    },
-    /**
-     * Returns the difference between 2 paths
-     * E.g. url = a/ baseUrl = a/b/ returns ../
-     * url = a/b/ baseUrl = a/ returns b/
-     * Provided by AbstractFileManager
-     * @param {string} url
-     * @param {string} baseUrl
-     * @returns {string}
-     */
-    pathDiff: function(url, baseUrl) {
-    },
-    /**
-     * Returns whether this file manager supports this file for syncronous file retrieval
-     * If true is returned, loadFileSync will then be called with the file.
-     * Provided by AbstractFileManager (returns false)
-     * @param {string} filename
-     * @param {string} currentDirectory
-     * @param {object} options
-     * @param {less.environment.environment} environment
-     * @returns {bool}
-     */
-    supportsSync: function(filename, currentDirectory, options, environment) {
-    },
-    /**
-     *
-     * @param {string} filename
-     * @param {string} currentDirectory
-     * @param {object} options
-     * @param {less.environment.environment} environment
-     * @returns {bool}
-     */
-    supports: function(filename, currentDirectory, options, environment) {
-    },
-    /**
-     * Loads a file asynchronously. Expects a promise that either rejects with an error or fulfills with an
-     * object containing
-     *  { filename: - full resolved path to file
-     *    contents: - the contents of the file, as a string }
-     *
-     * @param {string} filename
-     * @param {string} currentDirectory
-     * @param {object} options
-     * @param {less.environment.environment} environment
-     * @returns {Promise}
-     */
-    loadFile: function(filename, currentDirectory, options, environment) {
-    },
-    /**
-     * Loads a file synchronously. Expects an immediate return with an object containing
-     *  { error: - error object if an error occurs
-     *    filename: - full resolved path to file
-     *    contents: - the contents of the file, as a string }
-     *
-     * @param {string} filename
-     * @param {string} currentDirectory
-     * @param {object} options
-     * @param {less.environment.environment} environment
-     * @returns {object} should be an object containing error or contents and filename
-     */
-    loadFileSync: function(filename, currentDirectory, options, environment) {
-    }
-};
--- a/packages/less/src/less/environment/file-manager-api.ts
+++ b/packages/less/src/less/environment/file-manager-api.ts
@@ -0,0 +1,77 @@
+import type { Environment } from './environment-api'
+
+export interface FileManager {
+    /**
+     * Given the full path to a file, return the path component
+     * Provided by AbstractFileManager
+     */
+    getPath(filename: string): string
+    /**
+     * Append a .less extension if appropriate. Only called if less thinks one could be added.
+     * Provided by AbstractFileManager
+     */
+    tryAppendLessExtension(filename: string): string
+    /**
+     * Whether the rootpath should be converted to be absolute.
+     * The browser ovverides this to return true because urls must be absolute.
+     * Provided by AbstractFileManager (returns false)
+     */
+    alwaysMakePathsAbsolute(): boolean
+    /**
+     * Returns whether a path is absolute
+     * Provided by AbstractFileManager
+     */
+    isPathAbsolute(path: string): boolean
+    /**
+     * joins together 2 paths
+     * Provided by AbstractFileManager
+     */
+    join(basePath: string, laterPath: string): string
+    /**
+     * Returns the difference between 2 paths
+     * E.g. url = a/ baseUrl = a/b/ returns ../
+     * url = a/b/ baseUrl = a/ returns b/
+     * Provided by AbstractFileManager
+     */
+    pathDiff(url: string, baseUrl: string): string
+    /**
+     * Returns whether this file manager supports this file for syncronous file retrieval
+     * If true is returned, loadFileSync will then be called with the file.
+     * Provided by AbstractFileManager (returns false)
+     * 
+     * @todo - Narrow Options type
+     */
+    supportsSync(
+        filename: string,
+        currentDirectory: string,
+        options: Record<string, any>,
+        environment: Environment
+    ): boolean
+    /**
+     * If file manager supports async file retrieval for this file type
+     */
+    supports(
+        filename: string,
+        currentDirectory: string,
+        options: Record<string, any>,
+        environment: Environment
+    ): boolean
+    /**
+     * Loads a file asynchronously.
+     */
+    loadFile(
+        filename: string,
+        currentDirectory: string,
+        options: Record<string, any>,
+        environment: Environment
+    ): Promise<{ filename: string, contents: string }>
+    /**
+     * Loads a file synchronously. Expects an immediate return with an object
+     */
+    loadFileSync(
+        filename: string,
+        currentDirectory: string,
+        options: Record<string, any>,
+        environment: Environment
+    ): { error?: unknown, filename: string, contents: string }
+}
--- a/packages/less/src/less/functions/color-blending.js
+++ b/packages/less/src/less/functions/color-blending.js
@@ -76,6 +76,7 @@ const colorBlendModeFunctions = {
 };

 for (const f in colorBlendModeFunctions) {
+    // eslint-disable-next-line no-prototype-builtins
    if (colorBlendModeFunctions.hasOwnProperty(f)) {
        colorBlend[f] = colorBlend.bind(null, colorBlendModeFunctions[f]);
    }
--- a/packages/less/src/less/functions/color.js
+++ b/packages/less/src/less/functions/color.js
@@ -121,6 +121,25 @@ colorFunctions = {
        }
    },
    hsla: function (h, s, l, a) {
+        let m1;
+        let m2;
+
+        function hue(h) {
+            h = h < 0 ? h + 1 : (h > 1 ? h - 1 : h);
+            if (h * 6 < 1) {
+                return m1 + (m2 - m1) * h * 6;
+            }
+            else if (h * 2 < 1) {
+                return m2;
+            }
+            else if (h * 3 < 2) {
+                return m1 + (m2 - m1) * (2 / 3 - h) * 6;
+            }
+            else {
+                return m1;
+            }
+        }
+
        try {
            if (h instanceof Color) {
                if (s) {
@@ -131,25 +150,6 @@ colorFunctions = {
                return new Color(h.rgb, a, 'hsla');
            }

-            let m1;
-            let m2;
-
-            function hue(h) {
-                h = h < 0 ? h + 1 : (h > 1 ? h - 1 : h);
-                if (h * 6 < 1) {
-                    return m1 + (m2 - m1) * h * 6;
-                }
-                else if (h * 2 < 1) {
-                    return m2;
-                }
-                else if (h * 3 < 2) {
-                    return m1 + (m2 - m1) * (2 / 3 - h) * 6;
-                }
-                else {
-                    return m1;
-                }
-            }
-
            h = (number(h) % 360) / 360;
            s = clamp(number(s));l = clamp(number(l));a = clamp(number(a));

--- a/packages/less/src/less/functions/function-registry.js
+++ b/packages/less/src/less/functions/function-registry.js
@@ -6,6 +6,7 @@ function makeRegistry( base ) {
            // the registry by function-caller uses lower case as well.
            name = name.toLowerCase();

+            // eslint-disable-next-line no-prototype-builtins
            if (this._data.hasOwnProperty(name)) {
                // TODO warn
            }
--- a/packages/less/src/less/functions/list.js
+++ b/packages/less/src/less/functions/list.js
@@ -142,14 +142,14 @@ export default {
                    false, false, this.index, this.currentFileInfo));
            }

-            rules.push(new Ruleset([ new(Selector)([ new Element("", '&') ]) ],
+            rules.push(new Ruleset([ new(Selector)([ new Element('', '&') ]) ],
                newRules,
                rs.strictImports,
                rs.visibilityInfo()
            ));
        }

-        return new Ruleset([ new(Selector)([ new Element("", '&') ]) ],
+        return new Ruleset([ new(Selector)([ new Element('', '&') ]) ],
            rules,
            rs.strictImports,
            rs.visibilityInfo()
--- a/packages/less/src/less/functions/math.js
+++ b/packages/less/src/less/functions/math.js
@@ -15,6 +15,7 @@ const mathFunctions = {
 };

 for (const f in mathFunctions) {
+    // eslint-disable-next-line no-prototype-builtins
    if (mathFunctions.hasOwnProperty(f)) {
        mathFunctions[f] = mathHelper.bind(null, Math[f], mathFunctions[f]);
    }
--- a/packages/less/src/less/functions/svg.js
+++ b/packages/less/src/less/functions/svg.js
@@ -4,7 +4,7 @@ import Expression from '../tree/expression';
 import Quoted from '../tree/quoted';
 import URL from '../tree/url';

-export default environment => {
+export default () => {
    return { 'svg-gradient': function(direction) {
        let stops;
        let gradientDirectionSvg;
--- a/packages/less/src/less/import-manager.js
+++ b/packages/less/src/less/import-manager.js
@@ -180,4 +180,4 @@ export default function(environment) {
    }

    return ImportManager;
-};
+}
--- a/packages/less/src/less/index.js
+++ b/packages/less/src/less/index.js
@@ -95,4 +95,4 @@ export default function(environment, fileManagers) {
    initial.render = initial.render.bind(api);

    return api;
-};
+}
--- a/packages/less/src/less/less-error.js
+++ b/packages/less/src/less/less-error.js
@@ -62,8 +62,7 @@ const LessError = function(e, fileContentMap, currentFilename) {
                func();
            } catch (e) {
                const match = e.stack.match(anonymousFunc);
-                var line = parseInt(match[2]);
-                lineAdjust = 1 - line;
+                lineAdjust = 1 - parseInt(match[2]);
            }

            if (found) {
--- a/packages/less/src/less/parse-tree.js
+++ b/packages/less/src/less/parse-tree.js
@@ -54,7 +54,7 @@ export default function(SourceMapBuilder) {

            result.imports = [];
            for (const file in this.imports.files) {
-                if (this.imports.files.hasOwnProperty(file) && file !== this.imports.rootFilename) {
+                if (Object.prototype.hasOwnProperty.call(this.imports.files, file) && file !== this.imports.rootFilename) {
                    result.imports.push(file);
                }
            }
@@ -63,4 +63,4 @@ export default function(SourceMapBuilder) {
    }

    return ParseTree;
-};
+}
--- a/packages/less/src/less/parse.js
+++ b/packages/less/src/less/parse.js
@@ -39,7 +39,7 @@ export default function(environment, ParseTree, ImportManager) {
                rootFileInfo = options.rootFileInfo;
            } else {
                const filename = options.filename || 'input';
-                const entryPath = filename.replace(/[^\/\\]*$/, '');
+                const entryPath = filename.replace(/[^/\\]*$/, '');
                rootFileInfo = {
                    filename,
                    rewriteUrls: context.rewriteUrls,
@@ -84,4 +84,4 @@ export default function(environment, ParseTree, ImportManager) {
        }
    };
    return parse;
-};
+}
--- a/packages/less/src/less/parser/chunker.js
+++ b/packages/less/src/less/parser/chunker.js
@@ -119,4 +119,4 @@ export default function (input, fail) {

    emitChunk(true);
    return chunks;
-};
+}
--- a/packages/less/src/less/parser/parser-input.js
+++ b/packages/less/src/less/parser/parser-input.js
@@ -182,13 +182,14 @@ export default () => {
                case '\r':
                case '\n':
                    break;
-                case startChar:
+                case startChar: {
                    const str = input.substr(currentPosition, i + 1);
                    if (!loc && loc !== 0) {
                        skipWhitespace(i + 1);
                        return str
                    }
                    return [startChar, str];
+                }
                default:
            }
        }
@@ -220,7 +221,6 @@ export default () => {
        }

        do {
-            let prevChar;
            let nextChar = input.charAt(i);
            if (blockDepth === 0 && testChar(nextChar)) {
                returnVal = input.substr(lastPos, i - lastPos);
@@ -286,7 +286,7 @@ export default () => {
                        break;
                    case '}':
                    case ')':
-                    case ']':
+                    case ']': {
                        const expected = blockStack.pop();
                        if (nextChar === expected) {
                            blockDepth--;
@@ -296,13 +296,13 @@ export default () => {
                            returnVal = expected;
                            loop = false;
                        }
+                    }
                }
                i++;
                if (i > length) {
                    loop = false;
                }
            }
-            prevChar = nextChar;
        } while (loop);

        return returnVal ? returnVal : null;
--- a/packages/less/src/less/parser/parser.js
+++ b/packages/less/src/less/parser/parser.js
@@ -154,7 +154,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                        error('@plugin statements are not allowed when disablePluginRule is set to true');
                    }
                }
-            };
+            }

            globalVars = (additionalData && additionalData.globalVars) ? `${Parser.serializeVars(additionalData.globalVars)}\n` : '';
            modifyVars = (additionalData && additionalData.modifyVars) ? `\n${Parser.serializeVars(additionalData.modifyVars)}` : '';
@@ -422,7 +422,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {

                    parserInput.save();

-                    name = parserInput.$re(/^([\w-]+|%|~|progid:[\w\.]+)\(/);
+                    name = parserInput.$re(/^([\w-]+|%|~|progid:[\w.]+)\(/);
                    if (!name) {
                        parserInput.forget();
                        return;
@@ -576,7 +576,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                    }

                    value = this.quoted() || this.variable() || this.property() ||
-                            parserInput.$re(/^(?:(?:\\[\(\)'"])|[^\(\)'"])+/) || '';
+                            parserInput.$re(/^(?:(?:\\[()'"])|[^()'"])+/) || '';

                    parserInput.autoCommentAbsorb = true;

@@ -661,7 +661,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                    let rgb;
                    parserInput.save();

-                    if (parserInput.currentChar() === '#' && (rgb = parserInput.$re(/^#([A-Fa-f0-9]{8}|[A-Fa-f0-9]{6}|[A-Fa-f0-9]{3,4})([\w.#\[])?/))) {
+                    if (parserInput.currentChar() === '#' && (rgb = parserInput.$re(/^#([A-Fa-f0-9]{8}|[A-Fa-f0-9]{6}|[A-Fa-f0-9]{3,4})([\w.#[])?/))) {
                        if (!rgb[2]) {
                            parserInput.forget();
                            return new(tree.Color)(rgb[1], undefined, rgb[0]);
@@ -712,7 +712,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                unicodeDescriptor: function () {
                    let ud;

-                    ud = parserInput.$re(/^U\+[0-9a-fA-F?]+(\-[0-9a-fA-F?]+)?/);
+                    ud = parserInput.$re(/^U\+[0-9a-fA-F?]+(-[0-9a-fA-F?]+)?/);
                    if (ud) {
                        return new(tree.UnicodeDescriptor)(ud[0]);
                    }
@@ -1161,7 +1161,6 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {

                ruleLookups: function() {
                    let rule;
-                    let args;
                    const lookups = [];

                    if (parserInput.currentChar() !== '[') {
@@ -1170,7 +1169,6 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {

                    while (true) {
                        parserInput.save();
-                        args = null;
                        rule = this.lookupValue();
                        if (!rule && rule !== '') {
                            parserInput.restore();
@@ -1268,9 +1266,10 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                c = this.combinator();

                e = parserInput.$re(/^(?:\d+\.\d+|\d+)%/) ||
+                    // eslint-disable-next-line no-control-regex
                    parserInput.$re(/^(?:[.#]?|:*)(?:[\w-]|[^\x00-\x9f]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+/) ||
                    parserInput.$char('*') || parserInput.$char('&') || this.attribute() ||
-                    parserInput.$re(/^\([^&()@]+\)/) ||  parserInput.$re(/^[\.#:](?=@)/) ||
+                    parserInput.$re(/^\([^&()@]+\)/) ||  parserInput.$re(/^[.#:](?=@)/) ||
                    this.entities.variableCurly();

                if (!e) {
@@ -1389,11 +1388,11 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                    }
                    parserInput.commentStore.length = 0;
                    if (s.condition && selectors.length > 1) {
-                        error("Guards are only currently allowed on a single selector.");
+                        error('Guards are only currently allowed on a single selector.');
                    }
                    if (!parserInput.$char(',')) { break; }
                    if (s.condition) {
-                        error("Guards are only currently allowed on a single selector.");
+                        error('Guards are only currently allowed on a single selector.');
                    }
                    parserInput.commentStore.length = 0;
                }
@@ -1413,7 +1412,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                let cif;

                if (!(key = entities.variableCurly())) {
-                    key = expect(/^(?:[_A-Za-z0-9-\*]*\|)?(?:[_A-Za-z0-9-]|\\.)+/);
+                    key = expect(/^(?:[_A-Za-z0-9-*]*\|)?(?:[_A-Za-z0-9-]|\\.)+/);
                }

                op = parserInput.$re(/^[|~*$^]?=/);
@@ -1580,7 +1579,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
            },
            anonymousValue: function () {
                const index = parserInput.i;
-                const match = parserInput.$re(/^([^.#@\$+\/'"*`(;{}-]*);/);
+                const match = parserInput.$re(/^([^.#@$+/'"*`(;{}-]*);/);
                if (match) {
                    return new(tree.Anonymous)(match[1], index + currentIndex);
                }
@@ -1890,7 +1889,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                    parserInput.restore();
                    return null;
                }
-                const args = parserInput.$re(/^\s*([^\);]+)\)\s*/);
+                const args = parserInput.$re(/^\s*([^);]+)\)\s*/);
                if (args[1]) {
                    parserInput.forget();
                    return args[1].trim();
@@ -2057,7 +2056,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                if (m) {
                    isSpaced = parserInput.isWhitespace(-1);
                    while (true) {
-                        if (parserInput.peek(/^\/[*\/]/)) {
+                        if (parserInput.peek(/^\/[*/]/)) {
                            break;
                        }

@@ -2232,7 +2231,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                parserInput.forget();
                return body;
            },
-            atomicCondition: function (needsParens) {
+            atomicCondition: function () {
                const entities = this.entities;
                const index = parserInput.i;
                let a;
@@ -2240,10 +2239,9 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                let c;
                let op;

-                function cond() {
+                const cond = (function() {
                    return this.addition() || entities.keyword() || entities.quoted() || entities.mixinLookup();
-                }
-                cond = cond.bind(this);
+                }).bind(this)

                a = cond();
                if (a) {
@@ -2292,7 +2290,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                const entities = this.entities;
                let negate;

-                if (parserInput.peek(/^-[@\$\(]/)) {
+                if (parserInput.peek(/^-[@$(]/)) {
                    negate = parserInput.$char('-');
                }

@@ -2338,7 +2336,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                    if (e) {
                        entities.push(e);
                        // operations do not allow keyword "/" dimension (e.g. small/20px) so we support that here
-                        if (!parserInput.peek(/^\/[\/*]/)) {
+                        if (!parserInput.peek(/^\/[/*]/)) {
                            delim = parserInput.$char('/');
                            if (delim) {
                                entities.push(new(tree.Anonymous)(delim, index + currentIndex));
@@ -2382,7 +2380,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {

                match(/^(\*?)/);
                while (true) {
-                    if (!match(/^((?:[\w-]+)|(?:[@\$]\{[\w-]+\}))/)) {
+                    if (!match(/^((?:[\w-]+)|(?:[@$]\{[\w-]+\}))/)) {
                        break;
                    }
                }
--- a/packages/less/src/less/render.js
+++ b/packages/less/src/less/render.js
@@ -1,6 +1,6 @@
 import * as utils from './utils';

-export default function(environment, ParseTree, ImportManager) {
+export default function(environment, ParseTree) {
    const render = function (input, options, callback) {
        if (typeof options === 'function') {
            callback = options;
@@ -38,4 +38,4 @@ export default function(environment, ParseTree, ImportManager) {
    };

    return render;
-};
+}
--- a/packages/less/src/less/source-map-builder.js
+++ b/packages/less/src/less/source-map-builder.js
@@ -79,4 +79,4 @@ export default function (SourceMapOutput, environment) {
    }

    return SourceMapBuilder;
-};
+}
--- a/packages/less/src/less/source-map-output.js
+++ b/packages/less/src/less/source-map-output.js
@@ -116,6 +116,7 @@ export default function (environment) {

            if (this._outputSourceFiles) {
                for (const filename in this._contentsMap) {
+                    // eslint-disable-next-line no-prototype-builtins
                    if (this._contentsMap.hasOwnProperty(filename)) {
                        let source = this._contentsMap[filename];
                        if (this._contentsIgnoredCharsMap[filename]) {
@@ -147,4 +148,4 @@ export default function (environment) {
    }

    return SourceMapOutput;
-};
+}
--- a/packages/less/src/less/transform-tree.js
+++ b/packages/less/src/less/transform-tree.js
@@ -54,7 +54,7 @@ export default function(root, options) {
     */
    if (options.pluginManager) {
        visitorIterator = options.pluginManager.visitor();
-        for (var i = 0; i < 2; i++) {
+        for (let i = 0; i < 2; i++) {
            visitorIterator.first();
            while ((v = visitorIterator.get())) {
                if (v.isPreEvalVisitor) {
@@ -79,7 +79,7 @@ export default function(root, options) {

    evaldRoot = root.eval(evalEnv);

-    for (var i = 0; i < visitors.length; i++) {
+    for (let i = 0; i < visitors.length; i++) {
        visitors[i].run(evaldRoot);
    }

@@ -94,4 +94,4 @@ export default function(root, options) {
    }

    return evaldRoot;
-};
+}
--- a/packages/less/src/less/tree/attribute.js
+++ b/packages/less/src/less/tree/attribute.js
@@ -32,7 +32,7 @@ Attribute.prototype = Object.assign(new Node(), {
        }

        if (this.cif) {
-            value = value + " " + this.cif;
+            value = value + ' ' + this.cif;
        }

        return `[${value}]`;
--- a/packages/less/src/less/tree/call.js
+++ b/packages/less/src/less/tree/call.js
@@ -58,6 +58,7 @@ Call.prototype = Object.assign(new Node(), {
                result = funcCaller.call(this.args);
                exitCalc();
            } catch (e) {
+                // eslint-disable-next-line no-prototype-builtins
                if (e.hasOwnProperty('line') && e.hasOwnProperty('column')) {
                    throw e;
                }
--- a/packages/less/src/less/tree/color.js
+++ b/packages/less/src/less/tree/color.js
@@ -96,6 +96,7 @@ Color.prototype = Object.assign(new Node(), {
                break;
            case 'hsla':
                args.push(clamp(alpha, 1));
+            // eslint-disable-next-line no-fallthrough
            case 'hsl':
                color = this.toHSL();
                args = [
@@ -212,6 +213,7 @@ Color.prototype = Object.assign(new Node(), {
 Color.fromKeyword = function(keyword) {
    let c;
    const key = keyword.toLowerCase();
+    // eslint-disable-next-line no-prototype-builtins
    if (colors.hasOwnProperty(key)) {
        c = new Color(colors[key].slice(1));
    }
--- a/packages/less/src/less/tree/debug-info.js
+++ b/packages/less/src/less/tree/debug-info.js
@@ -7,9 +7,9 @@ function asMediaQuery(ctx) {
    if (!/^[a-z]+:\/\//i.test(filenameWithProtocol)) {
        filenameWithProtocol = `file://${filenameWithProtocol}`;
    }
-    return `@media -sass-debug-info{filename{font-family:${filenameWithProtocol.replace(/([.:\/\\])/g, function (a) {
+    return `@media -sass-debug-info{filename{font-family:${filenameWithProtocol.replace(/([.:/\\])/g, function (a) {
        if (a == '\\') {
-            a = '\/';
+            a = '/';
        }
        return `\\${a}`;
    })}}line{font-family:\\00003${ctx.debugInfo.lineNumber}}}\n`;
--- a/packages/less/src/less/tree/dimension.js
+++ b/packages/less/src/less/tree/dimension.js
@@ -1,3 +1,4 @@
+/* eslint-disable no-prototype-builtins */
 import Node from './node';
 import unitConversions from '../data/unit-conversions';
 import Unit from './unit';
@@ -23,6 +24,8 @@ Dimension.prototype = Object.assign(new Node(), {
        this.unit = visitor.visit(this.unit);
    },

+    // remove when Nodes have JSDoc types
+    // eslint-disable-next-line no-unused-vars
    eval(context) {
        return this;
    },
@@ -81,7 +84,7 @@ Dimension.prototype = Object.assign(new Node(), {
                other = other.convertTo(this.unit.usedUnits());

                if (context.strictUnits && other.unit.toString() !== unit.toString()) {
-                    throw new Error(`Incompatible units. Change the units or use the unit function. `
+                    throw new Error('Incompatible units. Change the units or use the unit function. '
                        + `Bad units: '${unit.toString()}' and '${other.unit.toString()}'.`);
                }

@@ -144,7 +147,6 @@ Dimension.prototype = Object.assign(new Node(), {
            conversions = derivedConversions;
        }
        applyUnit = function (atomicUnit, denominator) {
-            /* jshint loopfunc:true */
            if (group.hasOwnProperty(atomicUnit)) {
                if (denominator) {
                    value = value / (group[atomicUnit] / group[targetUnit]);
--- a/packages/less/src/less/tree/extend.js
+++ b/packages/less/src/less/tree/extend.js
@@ -35,6 +35,8 @@ Extend.prototype = Object.assign(new Node(), {
        return new Extend(this.selector.eval(context), this.option, this.getIndex(), this.fileInfo(), this.visibilityInfo());
    },

+    // remove when Nodes have JSDoc types
+    // eslint-disable-next-line no-unused-vars
    clone(context) {
        return new Extend(this.selector, this.option, this.getIndex(), this.fileInfo(), this.visibilityInfo());
    },
--- a/packages/less/src/less/tree/import.js
+++ b/packages/less/src/less/tree/import.js
@@ -31,7 +31,7 @@ const Import = function(path, features, options, index, currentFileInfo, visibil
        this.css = !this.options.less || this.options.inline;
    } else {
        const pathValue = this.getPath();
-        if (pathValue && /[#\.\&\?]css([\?;].*)?$/.test(pathValue)) {
+        if (pathValue && /[#.&?]css([?;].*)?$/.test(pathValue)) {
            this.css = true;
        }
    }
--- a/packages/less/src/less/tree/js-eval-node.js
+++ b/packages/less/src/less/tree/js-eval-node.js
@@ -29,8 +29,8 @@ JsEvalNode.prototype = Object.assign(new Node(), {

        const variables = context.frames[0].variables();
        for (const k in variables) {
+            // eslint-disable-next-line no-prototype-builtins
            if (variables.hasOwnProperty(k)) {
-                /* jshint loopfunc:true */
                evalContext[k.slice(1)] = {
                    value: variables[k].value,
                    toJS: function () {
--- a/packages/less/src/less/tree/namespace-value.js
+++ b/packages/less/src/less/tree/namespace-value.js
@@ -14,7 +14,7 @@ NamespaceValue.prototype = Object.assign(new Node(), {
    type: 'NamespaceValue',

    eval(context) {
-        let i, j, name, rules = this.value.eval(context);
+        let i, name, rules = this.value.eval(context);
        
        for (i = 0; i < this.lookups.length; i++) {
            name = this.lookups[i];
--- a/packages/less/src/less/tree/node.js
+++ b/packages/less/src/less/tree/node.js
@@ -1,10 +1,8 @@
-import * as utils from '../utils';
-
 /**
 * The reason why Node is a class and other nodes simply do not extend
 * from Node (since we're transpiling) is due to this issue:
 * 
- * https://github.com/less/less.js/issues/3434
+ * @see https://github.com/less/less.js/issues/3434
 */
 class Node {
    constructor() {
@@ -50,6 +48,8 @@ class Node {
    toCSS(context) {
        const strs = [];
        this.genCSS(context, {
+            // remove when genCSS has JSDoc types
+            // eslint-disable-next-line no-unused-vars
            add: function(chunk, fileInfo, index) {
                strs.push(chunk);
            },
--- a/packages/less/src/less/tree/quoted.js
+++ b/packages/less/src/less/tree/quoted.js
@@ -1,8 +1,6 @@
 import Node from './node';
 import Variable from './variable';
 import Property from './property';
-import * as utils from '../utils';
-

 const Quoted = function(str, content, escaped, index, currentFileInfo) {
    this.escaped = (escaped === undefined) ? true : escaped;
--- a/packages/less/src/less/tree/ruleset.js
+++ b/packages/less/src/less/tree/ruleset.js
@@ -45,7 +45,6 @@ Ruleset.prototype = Object.assign(new Node(), {
    },

    eval(context) {
-        const that = this;
        let selectors;
        let selCnt;
        let selector;
@@ -62,7 +61,7 @@ Ruleset.prototype = Object.assign(new Node(), {

            for (i = 0; i < selCnt; i++) {
                selector = this.selectors[i].eval(context);
-                for (var j = 0; j < selector.elements.length; j++) {
+                for (let j = 0; j < selector.elements.length; j++) {
                    if (selector.elements[j].isVariable) {
                        hasVariable = true;
                        break;
@@ -84,7 +83,7 @@ Ruleset.prototype = Object.assign(new Node(), {
                const selectorFileInfo = selectors[0].fileInfo();
                new Parser(context, this.parse.importManager, selectorFileInfo, startingIndex).parseNode(
                    toParseSelectors.join(','),
-                    ["selectors"],
+                    ['selectors'],
                    function(err, result) {
                        if (result) {
                            selectors = utils.flattenArray(result);
@@ -201,7 +200,7 @@ Ruleset.prototype = Object.assign(new Node(), {
                if (rule.selectors[0] && rule.selectors[0].isJustParentSelector()) {
                    rsRules.splice(i--, 1);

-                    for (var j = 0; (subRule = rule.rules[j]); j++) {
+                    for (let j = 0; (subRule = rule.rules[j]); j++) {
                        if (subRule instanceof Node) {
                            subRule.copyVisibilityInfo(rule.visibilityInfo());
                            if (!(subRule instanceof Declaration) || !subRule.variable) {
@@ -296,6 +295,7 @@ Ruleset.prototype = Object.assign(new Node(), {
                if (r.type === 'Import' && r.root && r.root.variables) {
                    const vars = r.root.variables();
                    for (const name in vars) {
+                        // eslint-disable-next-line no-prototype-builtins
                        if (vars.hasOwnProperty(name)) {
                            hash[name] = r.root.variable(name);
                        }
--- a/packages/less/src/less/tree/selector.js
+++ b/packages/less/src/less/tree/selector.js
@@ -95,7 +95,7 @@ Selector.prototype = Object.assign(new Node(), {

        let elements = this.elements.map( function(v) {
            return v.combinator.value + (v.value.value || v.value);
-        }).join('').match(/[,&#\*\.\w-]([\w-]|(\\.))*/g);
+        }).join('').match(/[,&#*.\w-]([\w-]|(\\.))*/g);

        if (elements) {
            if (elements[0] === '&') {
--- a/packages/less/src/less/tree/unit.js
+++ b/packages/less/src/less/tree/unit.js
@@ -78,7 +78,7 @@ Unit.prototype = Object.assign(new Node(), {
        let groupName;

        mapUnit = function (atomicUnit) {
-            /* jshint loopfunc:true */
+            // eslint-disable-next-line no-prototype-builtins
            if (group.hasOwnProperty(atomicUnit) && !result[groupName]) {
                result[groupName] = atomicUnit;
            }
@@ -87,6 +87,7 @@ Unit.prototype = Object.assign(new Node(), {
        };

        for (groupName in unitConversions) {
+            // eslint-disable-next-line no-prototype-builtins
            if (unitConversions.hasOwnProperty(groupName)) {
                group = unitConversions[groupName];

@@ -116,6 +117,7 @@ Unit.prototype = Object.assign(new Node(), {
        this.denominator = [];

        for (atomicUnit in counter) {
+            // eslint-disable-next-line no-prototype-builtins
            if (counter.hasOwnProperty(atomicUnit)) {
                const count = counter[atomicUnit];

--- a/packages/less/src/less/tree/url.js
+++ b/packages/less/src/less/tree/url.js
@@ -1,7 +1,7 @@
 import Node from './node';

 function escapePath(path) {
-    return path.replace(/[\(\)'"\s]/g, function(match) { return `\\${match}`; });
+    return path.replace(/[()'"\s]/g, function(match) { return `\\${match}`; });
 }

 const URL = function(val, index, currentFileInfo, isEvald) {
@@ -33,7 +33,7 @@ URL.prototype = Object.assign(new Node(), {
            rootpath = this.fileInfo() && this.fileInfo().rootpath;
            if (typeof rootpath === 'string' &&
                typeof val.value === 'string' &&
-                context.pathRequiresRewrite(val.value)) {
+                context.pathRequiresRewrite(val.value)) {
                if (!val.quote) {
                    rootpath = escapePath(rootpath);
                }
--- a/packages/less/src/less/utils.js
+++ b/packages/less/src/less/utils.js
@@ -35,7 +35,7 @@ export function copyArray(arr) {
 export function clone(obj) {
    const cloned = {};
    for (const prop in obj) {
-        if (obj.hasOwnProperty(prop)) {
+        if (Object.prototype.hasOwnProperty.call(obj, prop)) {
            cloned[prop] = obj[prop];
        }
    }
@@ -100,7 +100,7 @@ export function copyOptions(obj1, obj2) {

 export function merge(obj1, obj2) {
    for (const prop in obj2) {
-        if (obj2.hasOwnProperty(prop)) {
+        if (Object.prototype.hasOwnProperty.call(obj2, prop)) {
            obj1[prop] = obj2[prop];
        }
    }
--- a/packages/less/src/less/visitors/extend-visitor.js
+++ b/packages/less/src/less/visitors/extend-visitor.js
@@ -1,3 +1,7 @@
+/* eslint-disable no-unused-vars */
+/**
+ * @todo - Remove unused when JSDoc types are added for visitor methods
+ */
 import tree from '../tree';
 import Visitor from './visitor';
 import logger from '../logger';
--- a/packages/less/src/less/visitors/import-visitor.js
+++ b/packages/less/src/less/visitors/import-visitor.js
@@ -1,3 +1,7 @@
+/* eslint-disable no-unused-vars */
+/**
+ * @todo - Remove unused when JSDoc types are added for visitor methods
+ */
 import contexts from '../contexts';
 import Visitor from './visitor';
 import ImportSequencer from './import-sequencer';
--- a/packages/less/src/less/visitors/join-selector-visitor.js
+++ b/packages/less/src/less/visitors/join-selector-visitor.js
@@ -1,3 +1,7 @@
+/* eslint-disable no-unused-vars */
+/**
+ * @todo - Remove unused when JSDoc types are added for visitor methods
+ */
 import Visitor from './visitor';

 class JoinSelectorVisitor {
--- a/packages/less/src/less/visitors/to-css-visitor.js
+++ b/packages/less/src/less/visitors/to-css-visitor.js
@@ -1,3 +1,7 @@
+/* eslint-disable no-unused-vars */
+/**
+ * @todo - Remove unused when JSDoc types are added for visitor methods
+ */
 import tree from '../tree';
 import Visitor from './visitor';

--- a/packages/less/test/browser/generator/benchmark.config.js
+++ b/packages/less/test/browser/generator/benchmark.config.js
@@ -3,48 +3,48 @@ module.exports = {
    current: {
    // src is used to build list of less files to compile
        src: [
-            "benchmark/benchmark.less"
+            'benchmark/benchmark.less'
        ],
        options: {
-            helpers: "benchmark/browseroptions.js",
-            specs: "benchmark/browserspec.js",
-            outfile: "tmp/browser/test-runner-benchmark-current.html"
+            helpers: 'benchmark/browseroptions.js',
+            specs: 'benchmark/browserspec.js',
+            outfile: 'tmp/browser/test-runner-benchmark-current.html'
        }
    },
    v3_10_3: {
        // src is used to build list of less files to compile
        src: [
-            "benchmark/benchmark.less"
+            'benchmark/benchmark.less'
        ],
        options: {
-            helpers: "benchmark/browseroptions.js",
-            specs: "benchmark/browserspec.js",
-            outfile: "tmp/browser/test-runner-benchmark-v3_10_3.html",
-            less: "https://cdnjs.cloudflare.com/ajax/libs/less.js/3.10.3/less.min.js"
+            helpers: 'benchmark/browseroptions.js',
+            specs: 'benchmark/browserspec.js',
+            outfile: 'tmp/browser/test-runner-benchmark-v3_10_3.html',
+            less: 'https://cdnjs.cloudflare.com/ajax/libs/less.js/3.10.3/less.min.js'
        }
    },
    v3_9_0: {
        // src is used to build list of less files to compile
        src: [
-            "benchmark/benchmark.less"
+            'benchmark/benchmark.less'
        ],
        options: {
-            helpers: "benchmark/browseroptions.js",
-            specs: "benchmark/browserspec.js",
-            outfile: "tmp/browser/test-runner-benchmark-v3_9_0.html",
-            less: "https://cdnjs.cloudflare.com/ajax/libs/less.js/3.9.0/less.min.js"
+            helpers: 'benchmark/browseroptions.js',
+            specs: 'benchmark/browserspec.js',
+            outfile: 'tmp/browser/test-runner-benchmark-v3_9_0.html',
+            less: 'https://cdnjs.cloudflare.com/ajax/libs/less.js/3.9.0/less.min.js'
        }
    },
    v2_7_3: {
        // src is used to build list of less files to compile
        src: [
-            "benchmark/benchmark.less"
+            'benchmark/benchmark.less'
        ],
        options: {
-            helpers: "benchmark/browseroptions.js",
-            specs: "benchmark/browserspec.js",
-            outfile: "tmp/browser/test-runner-benchmark-v2_7_3.html",
-            less: "https://cdnjs.cloudflare.com/ajax/libs/less.js/2.7.3/less.min.js"
+            helpers: 'benchmark/browseroptions.js',
+            specs: 'benchmark/browserspec.js',
+            outfile: 'tmp/browser/test-runner-benchmark-v2_7_3.html',
+            less: 'https://cdnjs.cloudflare.com/ajax/libs/less.js/2.7.3/less.min.js'
        }
    }
 }
--- a/packages/less/test/browser/generator/runner.config.js
+++ b/packages/less/test/browser/generator/runner.config.js
@@ -19,168 +19,168 @@ module.exports = {
            `!${lessFolder}/_main/empty.less`
        ],
        options: {
-            helpers: "test/browser/runner-main-options.js",
-            specs: "test/browser/runner-main-spec.js",
-            outfile: "tmp/browser/test-runner-main.html"
+            helpers: 'test/browser/runner-main-options.js',
+            specs: 'test/browser/runner-main-spec.js',
+            outfile: 'tmp/browser/test-runner-main.html'
        }
    },
    legacy: {
        src: [`${lessFolder}/legacy/*.less`],
        options: {
-            helpers: "test/browser/runner-legacy-options.js",
-            specs: "test/browser/runner-legacy-spec.js",
-            outfile: "tmp/browser/test-runner-legacy.html"
+            helpers: 'test/browser/runner-legacy-options.js',
+            specs: 'test/browser/runner-legacy-spec.js',
+            outfile: 'tmp/browser/test-runner-legacy.html'
        }
    },
    strictUnits: {
        src: [`${lessFolder}/strict-units/*.less`],
        options: {
-            helpers: "test/browser/runner-strict-units-options.js",
-            specs: "test/browser/runner-strict-units-spec.js",
-            outfile: "tmp/browser/test-runner-strict-units.html"
+            helpers: 'test/browser/runner-strict-units-options.js',
+            specs: 'test/browser/runner-strict-units-spec.js',
+            outfile: 'tmp/browser/test-runner-strict-units.html'
        }
    },
    errors: {
        src: [
            `${lessFolder}/errors/*.less`,
            `${testFolder}/errors/javascript-error.less`,
-            "test/browser/less/errors/*.less"
+            'test/browser/less/errors/*.less'
        ],
        options: {
            timeout: 20000,
-            helpers: "test/browser/runner-errors-options.js",
-            specs: "test/browser/runner-errors-spec.js",
-            outfile: "tmp/browser/test-runner-errors.html"
+            helpers: 'test/browser/runner-errors-options.js',
+            specs: 'test/browser/runner-errors-spec.js',
+            outfile: 'tmp/browser/test-runner-errors.html'
        }
    },
    noJsErrors: {
        src: [`${lessFolder}/no-js-errors/*.less`],
        options: {
-            helpers: "test/browser/runner-no-js-errors-options.js",
-            specs: "test/browser/runner-no-js-errors-spec.js",
-            outfile: "tmp/browser/test-runner-no-js-errors.html"
+            helpers: 'test/browser/runner-no-js-errors-options.js',
+            specs: 'test/browser/runner-no-js-errors-spec.js',
+            outfile: 'tmp/browser/test-runner-no-js-errors.html'
        }
    },
    browser: {
        src: [
-            "test/browser/less/*.less",
-            "test/browser/less/plugin/*.less"
+            'test/browser/less/*.less',
+            'test/browser/less/plugin/*.less'
        ],
        options: {
-            helpers: "test/browser/runner-browser-options.js",
-            specs: "test/browser/runner-browser-spec.js",
-            outfile: "tmp/browser/test-runner-browser.html"
+            helpers: 'test/browser/runner-browser-options.js',
+            specs: 'test/browser/runner-browser-spec.js',
+            outfile: 'tmp/browser/test-runner-browser.html'
        }
    },
    relativeUrls: {
-        src: ["test/browser/less/relative-urls/*.less"],
+        src: ['test/browser/less/relative-urls/*.less'],
        options: {
-            helpers: "test/browser/runner-relative-urls-options.js",
-            specs: "test/browser/runner-relative-urls-spec.js",
-            outfile: "tmp/browser/test-runner-relative-urls.html"
+            helpers: 'test/browser/runner-relative-urls-options.js',
+            specs: 'test/browser/runner-relative-urls-spec.js',
+            outfile: 'tmp/browser/test-runner-relative-urls.html'
        }
    },
    rewriteUrls: {
-        src: ["test/browser/less/rewrite-urls/*.less"],
+        src: ['test/browser/less/rewrite-urls/*.less'],
        options: {
-            helpers: "test/browser/runner-rewrite-urls-options.js",
-            specs: "test/browser/runner-rewrite-urls-spec.js",
-            outfile: "tmp/browser/test-runner-rewrite-urls.html"
+            helpers: 'test/browser/runner-rewrite-urls-options.js',
+            specs: 'test/browser/runner-rewrite-urls-spec.js',
+            outfile: 'tmp/browser/test-runner-rewrite-urls.html'
        }
    },
    rootpath: {
-        src: ["test/browser/less/rootpath/*.less"],
+        src: ['test/browser/less/rootpath/*.less'],
        options: {
-            helpers: "test/browser/runner-rootpath-options.js",
-            specs: "test/browser/runner-rootpath-spec.js",
-            outfile: "tmp/browser/test-runner-rootpath.html"
+            helpers: 'test/browser/runner-rootpath-options.js',
+            specs: 'test/browser/runner-rootpath-spec.js',
+            outfile: 'tmp/browser/test-runner-rootpath.html'
        }
    },
    rootpathRelative: {
-        src: ["test/browser/less/rootpath-relative/*.less"],
+        src: ['test/browser/less/rootpath-relative/*.less'],
        options: {
-            helpers: "test/browser/runner-rootpath-relative-options.js",
-            specs: "test/browser/runner-rootpath-relative-spec.js",
-            outfile: "tmp/browser/test-runner-rootpath-relative.html"
+            helpers: 'test/browser/runner-rootpath-relative-options.js',
+            specs: 'test/browser/runner-rootpath-relative-spec.js',
+            outfile: 'tmp/browser/test-runner-rootpath-relative.html'
        }
    },
    rootpathRewriteUrls: {
-        src: ["test/browser/less/rootpath-rewrite-urls/*.less"],
+        src: ['test/browser/less/rootpath-rewrite-urls/*.less'],
        options: {
            helpers:
-            "test/browser/runner-rootpath-rewrite-urls-options.js",
-            specs: "test/browser/runner-rootpath-rewrite-urls-spec.js",
+            'test/browser/runner-rootpath-rewrite-urls-options.js',
+            specs: 'test/browser/runner-rootpath-rewrite-urls-spec.js',
            outfile:
-            "tmp/browser/test-runner-rootpath-rewrite-urls.html"
+            'tmp/browser/test-runner-rootpath-rewrite-urls.html'
        }
    },
    production: {
-        src: ["test/browser/less/production/*.less"],
+        src: ['test/browser/less/production/*.less'],
        options: {
-            helpers: "test/browser/runner-production-options.js",
-            specs: "test/browser/runner-production-spec.js",
-            outfile: "tmp/browser/test-runner-production.html"
+            helpers: 'test/browser/runner-production-options.js',
+            specs: 'test/browser/runner-production-spec.js',
+            outfile: 'tmp/browser/test-runner-production.html'
        }
    },
    modifyVars: {
-        src: ["test/browser/less/modify-vars/*.less"],
+        src: ['test/browser/less/modify-vars/*.less'],
        options: {
-            helpers: "test/browser/runner-modify-vars-options.js",
-            specs: "test/browser/runner-modify-vars-spec.js",
-            outfile: "tmp/browser/test-runner-modify-vars.html"
+            helpers: 'test/browser/runner-modify-vars-options.js',
+            specs: 'test/browser/runner-modify-vars-spec.js',
+            outfile: 'tmp/browser/test-runner-modify-vars.html'
        }
    },
    globalVars: {
-        src: ["test/browser/less/global-vars/*.less"],
+        src: ['test/browser/less/global-vars/*.less'],
        options: {
-            helpers: "test/browser/runner-global-vars-options.js",
-            specs: "test/browser/runner-global-vars-spec.js",
-            outfile: "tmp/browser/test-runner-global-vars.html"
+            helpers: 'test/browser/runner-global-vars-options.js',
+            specs: 'test/browser/runner-global-vars-spec.js',
+            outfile: 'tmp/browser/test-runner-global-vars.html'
        }
    },
    postProcessorPlugin: {
        src: [`${lessFolder}/postProcessorPlugin/*.less`],
        options: {
            helpers: [
-                `test/plugins/postprocess/index.js`,
-                "test/browser/runner-postProcessorPlugin-options.js"
+                'test/plugins/postprocess/index.js',
+                'test/browser/runner-postProcessorPlugin-options.js'
            ],
-            specs: "test/browser/runner-postProcessorPlugin.js",
+            specs: 'test/browser/runner-postProcessorPlugin.js',
            outfile:
-            "tmp/browser/test-runner-post-processor-plugin.html"
+            'tmp/browser/test-runner-post-processor-plugin.html'
        }
    },
    preProcessorPlugin: {
        src: [`${lessFolder}/preProcessorPlugin/*.less`],
        options: {
            helpers: [
-                `test/plugins/preprocess/index.js`,
-                "test/browser/runner-preProcessorPlugin-options.js"
+                'test/plugins/preprocess/index.js',
+                'test/browser/runner-preProcessorPlugin-options.js'
            ],
-            specs: "test/browser/runner-preProcessorPlugin.js",
-            outfile: "tmp/browser/test-runner-pre-processor-plugin.html"
+            specs: 'test/browser/runner-preProcessorPlugin.js',
+            outfile: 'tmp/browser/test-runner-pre-processor-plugin.html'
        }
    },
    visitorPlugin: {
        src: [`${lessFolder}/visitorPlugin/*.less`],
        options: {
            helpers: [
-                `test/plugins/visitor/index.js`,
-                "test/browser/runner-VisitorPlugin-options.js"
+                'test/plugins/visitor/index.js',
+                'test/browser/runner-VisitorPlugin-options.js'
            ],
-            specs: "test/browser/runner-VisitorPlugin.js",
-            outfile: "tmp/browser/test-runner-visitor-plugin.html"
+            specs: 'test/browser/runner-VisitorPlugin.js',
+            outfile: 'tmp/browser/test-runner-visitor-plugin.html'
        }
    },
    filemanagerPlugin: {
        src: [`${lessFolder}/filemanagerPlugin/*.less`],
        options: {
            helpers: [
-                `test/plugins/filemanager/index.js`,
-                "test/browser/runner-filemanagerPlugin-options.js"
+                'test/plugins/filemanager/index.js',
+                'test/browser/runner-filemanagerPlugin-options.js'
            ],
-            specs: "test/browser/runner-filemanagerPlugin.js",
-            outfile: "tmp/browser/test-runner-filemanager-plugin.html"
+            specs: 'test/browser/runner-filemanagerPlugin.js',
+            outfile: 'tmp/browser/test-runner-filemanager-plugin.html'
        }
    }
 }
--- a/packages/less/test/browser/runner-rewrite-urls-spec.js
+++ b/packages/less/test/browser/runner-rewrite-urls-spec.js
@@ -1,3 +1,3 @@
-describe("less.js browser test - rewrite urls", function() {
+describe('less.js browser test - rewrite urls', function() {
    testLessEqualsInDocument();
 });
--- a/packages/less/test/plugins/filemanager/index.js
+++ b/packages/less/test/plugins/filemanager/index.js
@@ -1,7 +1,7 @@
 (function(exports) {
    var plugin = function(less) {
        var FileManager = less.FileManager, TestFileManager = new FileManager();
-        function TestFileManager() { };
+        function TestFileManager() { }
        TestFileManager.loadFile = function (filename, currentDirectory, options, environment, callback) {
            if (filename.match(/.*\.test$/)) {
                return less.environment.fileManagers[0].loadFile('colors.test', currentDirectory, options, environment, callback);
--- a/packages/less/test/test-es6.ts
+++ b/packages/less/test/test-es6.ts
@@ -2,16 +2,16 @@
 console.log('Testing ES6 imports...')

 import less from '..';
-let lessRender = less.render;
+const lessRender = less.render;

 // then I call lessRender on something
-let y = lessRender(`
+lessRender(`
 body {
    a: 1;
    b: 2;
    c: 30;
    d: 4;
-}`, {sourceMap: {}},  function(error, output) {
-  if (error)
-    console.error(error)
+}`, {sourceMap: {}},  function(error: any, output: any) {
+    if (error)
+        console.error(error)
 })
--- a/packages/less/tsconfig.build.json
+++ b/packages/less/tsconfig.build.json
@@ -0,0 +1,7 @@
+{
+  "extends": "./tsconfig",
+  "compilerOptions": {
+    "rootDir": "./src",
+  },
+  "include": ["src/**/*"]
+}
--- a/packages/less/tsconfig.json
+++ b/packages/less/tsconfig.json
@@ -1,12 +1,13 @@
 {
  "compilerOptions": {
    "outDir": "./lib",
-    "rootDir": "./src",
+    "rootDir": ".",
    "allowJs": true,
    "sourceMap": true,
    "inlineSources": true,
    "esModuleInterop": true,
    "importHelpers": true,
+    "noImplicitAny": true,
    "target": "ES5"
  },
  "ts-node": {
@@ -14,6 +15,6 @@
      "rootDir": "."
    }
  },
-  "include": ["src/**/*"],
-  "exclude": ["node_modules"]
+  "include": ["**/*"],
+  "exclude": ["node_modules", "lib/**/*"]
 }