diff --git a/src/grammar-registry.coffee b/src/grammar-registry.coffee
deleted file mode 100644
index a2341c967..000000000
--- a/src/grammar-registry.coffee
+++ /dev/null
@@ -1,130 +0,0 @@
-_ = require 'underscore-plus'
-FirstMate = require 'first-mate'
-Token = require './token'
-fs = require 'fs-plus'
-Grim = require 'grim'
-
-PathSplitRegex = new RegExp("[/.]")
-
-# Extended: Syntax class holding the grammars used for tokenizing.
-#
-# An instance of this class is always available as the `atom.grammars` global.
-#
-# The Syntax class also contains properties for things such as the
-# language-specific comment regexes. See {::getProperty} for more details.
-module.exports =
-class GrammarRegistry extends FirstMate.GrammarRegistry
-  constructor: ({@config}={}) ->
-    super(maxTokensPerLine: 100, maxLineLength: 1000)
-
-  createToken: (value, scopes) -> new Token({value, scopes})
-
-  # Extended: Select a grammar for the given file path and file contents.
-  #
-  # This picks the best match by checking the file path and contents against
-  # each grammar.
-  #
-  # * `filePath` A {String} file path.
-  # * `fileContents` A {String} of text for the file path.
-  #
-  # Returns a {Grammar}, never null.
-  selectGrammar: (filePath, fileContents) ->
-    @selectGrammarWithScore(filePath, fileContents).grammar
-
-  selectGrammarWithScore: (filePath, fileContents) ->
-    bestMatch = null
-    highestScore = -Infinity
-    for grammar in @grammars
-      score = @getGrammarScore(grammar, filePath, fileContents)
-      if score > highestScore or not bestMatch?
-        bestMatch = grammar
-        highestScore = score
-    {grammar: bestMatch, score: highestScore}
-
-  # Extended: Returns a {Number} representing how well the grammar matches the
-  # `filePath` and `contents`.
-  getGrammarScore: (grammar, filePath, contents) ->
-    contents = fs.readFileSync(filePath, 'utf8') if not contents? and fs.isFileSync(filePath)
-
-    score = @getGrammarPathScore(grammar, filePath)
-    if score > 0 and not grammar.bundledPackage
-      score += 0.25
-    if @grammarMatchesContents(grammar, contents)
-      score += 0.125
-    score
-
-  getGrammarPathScore: (grammar, filePath) ->
-    return -1 unless filePath
-    filePath = filePath.replace(/\\/g, '/') if process.platform is 'win32'
-
-    pathComponents = filePath.toLowerCase().split(PathSplitRegex)
-    pathScore = -1
-
-    fileTypes = grammar.fileTypes
-    if customFileTypes = @config.get('core.customFileTypes')?[grammar.scopeName]
-      fileTypes = fileTypes.concat(customFileTypes)
-
-    for fileType, i in fileTypes
-      fileTypeComponents = fileType.toLowerCase().split(PathSplitRegex)
-      pathSuffix = pathComponents[-fileTypeComponents.length..-1]
-      if _.isEqual(pathSuffix, fileTypeComponents)
-        pathScore = Math.max(pathScore, fileType.length)
-        if i >= grammar.fileTypes.length
-          pathScore += 0.5
-
-    pathScore
-
-  grammarMatchesContents: (grammar, contents) ->
-    return false unless contents? and grammar.firstLineRegex?
-
-    escaped = false
-    numberOfNewlinesInRegex = 0
-    for character in grammar.firstLineRegex.source
-      switch character
-        when '\\'
-          escaped = not escaped
-        when 'n'
-          numberOfNewlinesInRegex++ if escaped
-          escaped = false
-        else
-          escaped = false
-    lines = contents.split('\n')
-    grammar.firstLineRegex.testSync(lines[0..numberOfNewlinesInRegex].join('\n'))
-
-  # Deprecated: Get the grammar override for the given file path.
-  #
-  # * `filePath` A {String} file path.
-  #
-  # Returns a {String} such as `"source.js"`.
-  grammarOverrideForPath: (filePath) ->
-    Grim.deprecate 'Use atom.textEditors.getGrammarOverride(editor) instead'
-    if editor = getEditorForPath(filePath)
-      atom.textEditors.getGrammarOverride(editor)
-
-  # Deprecated: Set the grammar override for the given file path.
-  #
-  # * `filePath` A non-empty {String} file path.
-  # * `scopeName` A {String} such as `"source.js"`.
-  #
-  # Returns undefined
-  setGrammarOverrideForPath: (filePath, scopeName) ->
-    Grim.deprecate 'Use atom.textEditors.setGrammarOverride(editor, scopeName) instead'
-    if editor = getEditorForPath(filePath)
-      atom.textEditors.setGrammarOverride(editor, scopeName)
-    return
-
-  # Deprecated: Remove the grammar override for the given file path.
-  #
-  # * `filePath` A {String} file path.
-  #
-  # Returns undefined.
-  clearGrammarOverrideForPath: (filePath) ->
-    Grim.deprecate 'Use atom.textEditors.clearGrammarOverride(editor) instead'
-    if editor = getEditorForPath(filePath)
-      atom.textEditors.clearGrammarOverride(editor)
-    return
-
-getEditorForPath = (filePath) ->
-  if filePath?
-    atom.workspace.getTextEditors().find (editor) ->
-      editor.getPath() is filePath
diff --git a/src/grammar-registry.js b/src/grammar-registry.js
new file mode 100644
index 000000000..b1de16ba1
--- /dev/null
+++ b/src/grammar-registry.js
@@ -0,0 +1,171 @@
+const _ = require('underscore-plus')
+const FirstMate = require('first-mate')
+const Token = require('./token')
+const fs = require('fs-plus')
+const Grim = require('grim')
+
+const PathSplitRegex = new RegExp('[/.]')
+
+// Extended: Syntax class holding the grammars used for tokenizing.
+//
+// An instance of this class is always available as the `atom.grammars` global.
+//
+// The Syntax class also contains properties for things such as the
+// language-specific comment regexes. See {::getProperty} for more details.
+module.exports =
+class GrammarRegistry extends FirstMate.GrammarRegistry {
+  constructor ({config} = {}) {
+    super({maxTokensPerLine: 100, maxLineLength: 1000})
+    this.config = config
+  }
+
+  createToken (value, scopes) {
+    return new Token({value, scopes})
+  }
+
+  // Extended: Select a grammar for the given file path and file contents.
+  //
+  // This picks the best match by checking the file path and contents against
+  // each grammar.
+  //
+  // * `filePath` A {String} file path.
+  // * `fileContents` A {String} of text for the file path.
+  //
+  // Returns a {Grammar}, never null.
+  selectGrammar (filePath, fileContents) {
+    return this.selectGrammarWithScore(filePath, fileContents).grammar
+  }
+
+  selectGrammarWithScore (filePath, fileContents) {
+    let bestMatch = null
+    let highestScore = -Infinity
+    for (let grammar of this.grammars) {
+      const score = this.getGrammarScore(grammar, filePath, fileContents)
+      if ((score > highestScore) || (bestMatch == null)) {
+        bestMatch = grammar
+        highestScore = score
+      }
+    }
+    return {grammar: bestMatch, score: highestScore}
+  }
+
+  // Extended: Returns a {Number} representing how well the grammar matches the
+  // `filePath` and `contents`.
+  getGrammarScore (grammar, filePath, contents) {
+    if ((contents == null) && fs.isFileSync(filePath)) {
+      contents = fs.readFileSync(filePath, 'utf8')
+    }
+
+    let score = this.getGrammarPathScore(grammar, filePath)
+    if ((score > 0) && !grammar.bundledPackage) {
+      score += 0.25
+    }
+    if (this.grammarMatchesContents(grammar, contents)) {
+      score += 0.125
+    }
+    return score
+  }
+
+  getGrammarPathScore (grammar, filePath) {
+    if (!filePath) { return -1 }
+    if (process.platform === 'win32') { filePath = filePath.replace(/\\/g, '/') }
+
+    const pathComponents = filePath.toLowerCase().split(PathSplitRegex)
+    let pathScore = -1
+
+    let customFileTypes
+    if (this.config.get('core.customFileTypes')) {
+      customFileTypes = this.config.get('core.customFileTypes')[grammar.scopeName]
+    }
+
+    let { fileTypes } = grammar
+    if (customFileTypes) {
+      fileTypes = fileTypes.concat(customFileTypes)
+    }
+
+    for (let i = 0; i < fileTypes.length; i++) {
+      const fileType = fileTypes[i]
+      const fileTypeComponents = fileType.toLowerCase().split(PathSplitRegex)
+      const pathSuffix = pathComponents.slice(-fileTypeComponents.length)
+      if (_.isEqual(pathSuffix, fileTypeComponents)) {
+        pathScore = Math.max(pathScore, fileType.length)
+        if (i >= grammar.fileTypes.length) {
+          pathScore += 0.5
+        }
+      }
+    }
+
+    return pathScore
+  }
+
+  grammarMatchesContents (grammar, contents) {
+    if ((contents == null) || (grammar.firstLineRegex == null)) { return false }
+
+    let escaped = false
+    let numberOfNewlinesInRegex = 0
+    for (let character of grammar.firstLineRegex.source) {
+      switch (character) {
+        case '\\':
+          escaped = !escaped
+          break
+        case 'n':
+          if (escaped) { numberOfNewlinesInRegex++ }
+          escaped = false
+          break
+        default:
+          escaped = false
+      }
+    }
+    const lines = contents.split('\n')
+    return grammar.firstLineRegex.testSync(lines.slice(0, numberOfNewlinesInRegex + 1).join('\n'))
+  }
+
+  // Deprecated: Get the grammar override for the given file path.
+  //
+  // * `filePath` A {String} file path.
+  //
+  // Returns a {String} such as `"source.js"`.
+  grammarOverrideForPath (filePath) {
+    Grim.deprecate('Use atom.textEditors.getGrammarOverride(editor) instead')
+
+    const editor = getEditorForPath(filePath)
+    if (editor) {
+      return atom.textEditors.getGrammarOverride(editor)
+    }
+  }
+
+  // Deprecated: Set the grammar override for the given file path.
+  //
+  // * `filePath` A non-empty {String} file path.
+  // * `scopeName` A {String} such as `"source.js"`.
+  //
+  // Returns undefined.
+  setGrammarOverrideForPath (filePath, scopeName) {
+    Grim.deprecate('Use atom.textEditors.setGrammarOverride(editor, scopeName) instead')
+
+    const editor = getEditorForPath(filePath)
+    if (editor) {
+      atom.textEditors.setGrammarOverride(editor, scopeName)
+    }
+  }
+
+  // Deprecated: Remove the grammar override for the given file path.
+  //
+  // * `filePath` A {String} file path.
+  //
+  // Returns undefined.
+  clearGrammarOverrideForPath (filePath) {
+    Grim.deprecate('Use atom.textEditors.clearGrammarOverride(editor) instead')
+
+    const editor = getEditorForPath(filePath)
+    if (editor) {
+      atom.textEditors.clearGrammarOverride(editor)
+    }
+  }
+}
+
+function getEditorForPath (filePath) {
+  if (filePath != null) {
+    return atom.workspace.getTextEditors().find(editor => editor.getPath() === filePath)
+  }
+}