From f5cd2869d35268cc158409195b561b28feca5d94 Mon Sep 17 00:00:00 2001
From: David Walsh <dlwalsh@gmail.com>
Date: Tue, 4 Jul 2017 12:40:53 +1000
Subject: [PATCH] [guide] [eslint config] [base] [breaking] Rules prohibiting
 global isNaN, isFinite.

 - Update README with new Standard Library section.
---
 README.md                                     | 45 ++++++++++++++++++-
 .../rules/best-practices.js                   | 24 ++++++++++
 .../rules/variables.js                        |  3 +-
 3 files changed, 68 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index b9887ff2..4125081c 100644
--- a/README.md
+++ b/README.md
@@ -44,6 +44,7 @@ Other Style Guides
   1. [jQuery](#jquery)
   1. [ECMAScript 5 Compatibility](#ecmascript-5-compatibility)
   1. [ECMAScript 6+ (ES 2015+) Styles](#ecmascript-6-es-2015-styles)
+  1. [Standard Library](#standard-library)
   1. [Testing](#testing)
   1. [Performance](#performance)
   1. [Resources](#resources)
@@ -3148,10 +3149,50 @@ Other Style Guides
 
 **[⬆ back to top](#table-of-contents)**
 
+## Standard Library
+
+  The [Standard Library](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects)
+  contains utilities that are functionally broken but remain for legacy reasons.
+
+  <a name="standard-library--isnan"></a>
+  - [29.1](#standard-library--isnan) Use `Number.isNaN` instead of global `isNaN`.
+    eslint: [`no-restricted-globals`](http://eslint.org/docs/rules/no-restricted-globals)
+
+    > Why? The global `isNaN` coerces non-numbers to numbers, returning true for anything that coerces to NaN.
+    If this behavior is desired, make it explicit.
+
+    ```javascript
+    // bad
+    isNaN('1.2'); // false
+    isNaN('1.2.3'); // true
+
+    // good
+    Number.isNaN('1.2.3'); // false
+    Number.isNaN(Number('1.2.3')); // true
+    ```
+
+  <a name="standard-library--isfinite"></a>
+  - [29.2](#standard-library--isfinite) Use `Number.isFinite` instead of global `isFinite`.
+    eslint: [`no-restricted-globals`](http://eslint.org/docs/rules/no-restricted-globals)
+
+    > Why? The global `isFinite` coerces non-numbers to numbers, returning true for anything that coerces to a finite number.
+    If this behavior is desired, make it explicit.
+
+    ```javascript
+    // bad
+    isFinite('2e3'); // true
+
+    // good
+    Number.isFinite('2e3'); // false
+    Number.isFinite(parseInt('2e3', 10)); // true
+    ```
+
+**[⬆ back to top](#table-of-contents)**
+
 ## Testing
 
   <a name="testing--yup"></a><a name="28.1"></a>
-  - [29.1](#testing--yup) **Yup.**
+  - [30.1](#testing--yup) **Yup.**
 
     ```javascript
     function foo() {
@@ -3160,7 +3201,7 @@ Other Style Guides
     ```
 
   <a name="testing--for-real"></a><a name="28.2"></a>
-  - [29.2](#testing--for-real) **No, but seriously**:
+  - [30.2](#testing--for-real) **No, but seriously**:
     - Whichever testing framework you use, you should be writing tests!
     - Strive to write many small pure functions, and minimize where mutations occur.
     - Be cautious about stubs and mocks - they can make your tests more brittle.
diff --git a/packages/eslint-config-airbnb-base/rules/best-practices.js b/packages/eslint-config-airbnb-base/rules/best-practices.js
index 02ea3e23..11b18a2e 100644
--- a/packages/eslint-config-airbnb-base/rules/best-practices.js
+++ b/packages/eslint-config-airbnb-base/rules/best-practices.js
@@ -194,6 +194,30 @@ module.exports = {
       object: 'arguments',
       property: 'callee',
       message: 'arguments.callee is deprecated',
+    }, {
+      object: 'global',
+      property: 'isFinite',
+      message: 'Please use Number.isFinite instead',
+    }, {
+      object: 'self',
+      property: 'isFinite',
+      message: 'Please use Number.isFinite instead',
+    }, {
+      object: 'window',
+      property: 'isFinite',
+      message: 'Please use Number.isFinite instead',
+    }, {
+      object: 'global',
+      property: 'isNaN',
+      message: 'Please use Number.isNaN instead',
+    }, {
+      object: 'self',
+      property: 'isNaN',
+      message: 'Please use Number.isNaN instead',
+    }, {
+      object: 'window',
+      property: 'isNaN',
+      message: 'Please use Number.isNaN instead',
     }, {
       property: '__defineGetter__',
       message: 'Please use Object.defineProperty instead.',
diff --git a/packages/eslint-config-airbnb-base/rules/variables.js b/packages/eslint-config-airbnb-base/rules/variables.js
index fe38ea5d..805563a5 100644
--- a/packages/eslint-config-airbnb-base/rules/variables.js
+++ b/packages/eslint-config-airbnb-base/rules/variables.js
@@ -16,8 +16,7 @@ module.exports = {
     'no-label-var': 'error',
 
     // disallow specific globals
-    // TODO: enable, semver-major
-    'no-restricted-globals': ['off'].concat(restrictedGlobals),
+    'no-restricted-globals': ['error', 'isFinite', 'isNaN'].concat(restrictedGlobals),
 
     // disallow declaration of variables already declared in the outer scope
     'no-shadow': 'error',