diff --git a/src/babel.js b/src/babel.js
index 738433ed8..e44d78996 100644
--- a/src/babel.js
+++ b/src/babel.js
@@ -1,23 +1,33 @@
 'use strict'
 
-const _ = require('underscore-plus')
-const crypto = require('crypto')
-const path = require('path')
+var _ = require('underscore-plus')
+var crypto = require('crypto')
+var path = require('path')
+var defaultOptions = require('../static/babelrc.json')
 
-let babel = null
-let babelVersionDirectory = null
+var babel = null
+var babelVersionDirectory = null
 
-const defaultOptions = require('../static/babelrc.json')
+var PREFIXES = [
+  '/** @babel */',
+  '"use babel"',
+  '\'use babel\''
+]
+
+var PREFIX_LENGTH = Math.max.apply(Math, PREFIXES.map(function (prefix) {
+  return prefix.length
+}))
 
 exports.shouldCompile = function(sourceCode) {
-  return sourceCode.startsWith('/** @babel */') ||
-    sourceCode.startsWith('"use babel"') ||
-    sourceCode.startsWith("'use babel'")
+  var start = sourceCode.substr(0, PREFIX_LENGTH)
+  return PREFIXES.some(function (prefix) {
+    return start.indexOf(prefix) === 0
+  })
 }
 
 exports.getCachePath = function(sourceCode) {
   if (babelVersionDirectory == null) {
-    let babelVersion = require('babel-core/package.json').version
+    var babelVersion = require('babel-core/package.json').version
     babelVersionDirectory = path.join('js', 'babel', createVersionAndOptionsDigest(babelVersion, defaultOptions))
   }
 
@@ -35,7 +45,7 @@ exports.compile = function(sourceCode, filePath) {
     babel = require('babel-core')
   }
 
-  let options = _.defaults({filename: filePath}, defaultOptions)
+  var options = _.defaults({filename: filePath}, defaultOptions)
   return babel.transform(sourceCode, options).code
 }
 
diff --git a/src/coffee-script.js b/src/coffee-script.js
index 0aa428ab8..efdcbb72b 100644
--- a/src/coffee-script.js
+++ b/src/coffee-script.js
@@ -1,13 +1,13 @@
 'use strict'
 
-const crypto = require('crypto')
-const path = require('path')
+var crypto = require('crypto')
+var path = require('path')
 
 // The coffee-script compiler is required eagerly because:
 // 1. It is always used.
 // 2. It reassigns Error.prepareStackTrace, so we need to make sure that
 //    the 'source-map-support' module is installed *after* it is loaded.
-const CoffeeScript = require('coffee-script')
+var CoffeeScript = require('coffee-script')
 
 exports.shouldCompile = function() {
   return true
@@ -24,13 +24,13 @@ exports.getCachePath = function(sourceCode) {
 }
 
 exports.compile = function(sourceCode, filePath) {
-  let output = CoffeeScript.compile(sourceCode, {
+  var output = CoffeeScript.compile(sourceCode, {
     filename: filePath,
     sourceFiles: [filePath],
     sourceMap: true
   })
 
-  let js = output.js
+  var js = output.js
   js += '\n'
   js += '//# sourceMappingURL=data:application/json;base64,'
   js += new Buffer(output.v3SourceMap).toString('base64')
diff --git a/src/compile-cache.js b/src/compile-cache.js
index 821eac45e..0f2554efb 100644
--- a/src/compile-cache.js
+++ b/src/compile-cache.js
@@ -1,31 +1,31 @@
 'use strict'
 
-const path = require('path')
-const CSON = require('season')
-const fs = require('fs-plus')
+var path = require('path')
+var CSON = require('season')
+var fs = require('fs-plus')
+var _ = require('underscore-plus')
 
-const COMPILERS = {
+var COMPILERS = {
   '.js': require('./babel'),
   '.ts': require('./typescript'),
   '.coffee': require('./coffee-script')
 }
 
-for (let extension in COMPILERS) {
-  let compiler = COMPILERS[extension]
+var cacheDirectory = null
+
+_.each(COMPILERS, function (compiler, extension) {
   Object.defineProperty(require.extensions, extension, {
     enumerable: true,
     writable: false,
     value: function (module, filePath) {
-      let code = compileFileAtPath(compiler, filePath)
+      var code = compileFileAtPath(compiler, filePath, extension)
       return module._compile(code, filePath)
     }
   })
-}
-
-let cacheDirectory = null
+})
 
 exports.setAtomHomeDirectory = function (atomHome) {
-  let cacheDir = path.join(atomHome, 'compile-cache')
+  var cacheDir = path.join(atomHome, 'compile-cache')
   if (process.env.USER === 'root' && process.env.SUDO_USER && process.env.SUDO_USER !== process.env.USER) {
     cacheDir = path.join(cacheDirectory, 'root')
   }
@@ -43,21 +43,23 @@ exports.getCacheDirectory = function () {
 
 exports.addPathToCache = function (filePath, atomHome) {
   this.setAtomHomeDirectory(atomHome)
-  extension = path.extname(filePath)
-  if (extension === '.cson') {
-    return CSON.readFileSync(filePath)
-  }
+  var extension = path.extname(filePath)
 
-  if (compiler = COMPILERS[extension]) {
-    return compileFileAtPath(compiler, filePath)
+  if (extension === '.cson') {
+    CSON.readFileSync(filePath)
+  } else {
+    var compiler = COMPILERS[extension]
+    if (compiler) {
+      compileFileAtPath(compiler, filePath, extension)
+    }
   }
 }
 
-function compileFileAtPath (compiler, filePath) {
-  let sourceCode = fs.readFileSync(filePath, 'utf8')
+function compileFileAtPath (compiler, filePath, extension) {
+  var sourceCode = fs.readFileSync(filePath, 'utf8')
   if (compiler.shouldCompile(sourceCode, filePath)) {
-    let cachePath = compiler.getCachePath(sourceCode, filePath)
-    let compiledCode = readCachedJavascript(cachePath)
+    var cachePath = compiler.getCachePath(sourceCode, filePath)
+    var compiledCode = readCachedJavascript(cachePath)
     if (compiledCode == null) {
       compiledCode = compiler.compile(sourceCode, filePath)
       writeCachedJavascript(cachePath, compiledCode)
@@ -68,7 +70,7 @@ function compileFileAtPath (compiler, filePath) {
 }
 
 function readCachedJavascript (relativeCachePath) {
-  let cachePath = path.join(cacheDirectory, relativeCachePath)
+  var cachePath = path.join(cacheDirectory, relativeCachePath)
   if (fs.isFileSync(cachePath)) {
     try {
       return fs.readFileSync(cachePath, 'utf8')
@@ -78,11 +80,11 @@ function readCachedJavascript (relativeCachePath) {
 }
 
 function writeCachedJavascript (relativeCachePath, code) {
-  let cachePath = path.join(cacheDirectory, relativeCachePath)
+  var cachePath = path.join(cacheDirectory, relativeCachePath)
   fs.writeFileSync(cachePath, code, 'utf8')
 }
 
-const INLINE_SOURCE_MAP_REGEXP = /\/\/[#@]\s*sourceMappingURL=([^'"\n]+)\s*$/mg
+var INLINE_SOURCE_MAP_REGEXP = /\/\/[#@]\s*sourceMappingURL=([^'"\n]+)\s*$/mg
 
 require('source-map-support').install({
   handleUncaughtExceptions: false,
@@ -95,14 +97,14 @@ require('source-map-support').install({
       return null
     }
 
-    let sourceCode = fs.readFileSync(filePath, 'utf8')
-    let compiler = COMPILERS[path.extname(filePath)]
-    let fileData = readCachedJavascript(compiler.getCachePath(sourceCode, filePath))
+    var sourceCode = fs.readFileSync(filePath, 'utf8')
+    var compiler = COMPILERS[path.extname(filePath)]
+    var fileData = readCachedJavascript(compiler.getCachePath(sourceCode, filePath))
     if (fileData == null) {
       return null
     }
 
-    let match, lastMatch
+    var match, lastMatch
     INLINE_SOURCE_MAP_REGEXP.lastIndex = 0
     while ((match = INLINE_SOURCE_MAP_REGEXP.exec(fileData))) {
       lastMatch = match
@@ -111,9 +113,9 @@ require('source-map-support').install({
       return null
     }
 
-    let sourceMappingURL = lastMatch[1]
-    let rawData = sourceMappingURL.slice(sourceMappingURL.indexOf(',') + 1)
-    let sourceMap = JSON.parse(new Buffer(rawData, 'base64').toString())
+    var sourceMappingURL = lastMatch[1]
+    var rawData = sourceMappingURL.slice(sourceMappingURL.indexOf(',') + 1)
+    var sourceMap = JSON.parse(new Buffer(rawData, 'base64').toString())
 
     return {
       map: sourceMap,
diff --git a/src/typescript.js b/src/typescript.js
index c372c775b..967fdf18e 100644
--- a/src/typescript.js
+++ b/src/typescript.js
@@ -1,25 +1,25 @@
 'use strict'
 
-const _ = require('underscore-plus')
-const crypto = require('crypto')
-const path = require('path')
+var _ = require('underscore-plus')
+var crypto = require('crypto')
+var path = require('path')
 
-let TypeScriptSimple = null
-let typescriptVersionDir = null
-
-const defaultOptions = {
+var defaultOptions = {
   target: 1,
   module: 'commonjs',
   sourceMap: true
 }
 
+var TypeScriptSimple = null
+var typescriptVersionDir = null
+
 exports.shouldCompile = function() {
   return true
 }
 
 exports.getCachePath = function(sourceCode) {
   if (typescriptVersionDir == null) {
-    let version = require('typescript-simple/package.json').version
+    var version = require('typescript-simple/package.json').version
     typescriptVersionDir = path.join('ts', createVersionAndOptionsDigest(version, defaultOptions))
   }
 
@@ -37,7 +37,7 @@ exports.compile = function(sourceCode, filePath) {
     TypeScriptSimple = require('typescript-simple').TypeScriptSimple
   }
 
-  let options = _.defaults({filename: filePath}, defaultOptions)
+  var options = _.defaults({filename: filePath}, defaultOptions)
   return new TypeScriptSimple(options, false).compile(sourceCode, filePath)
 }