ECMAScript6

Status of ES6 support in Closure Compiler

Introduction

There are major changes in store for EcmaScript 6 and will require major changes to Closure Compiler to support it.

This is a place to collect changes that will need to be made to the compiler.

Overview

Summary: https://github.com/lukehoban/es6features

Spec: http://people.mozilla.org/~jorendorff/es6-draft.html

Details

Parser

The new parser is in place, and has replaced the old Rhino parser. It understands all ES6 features though there may still be a few bugs here and there.

Transpilation

We support transpilation of the following ES6 features down to ES3.

• let/const
• arrow functions
• default parameters and rest ("...") parameters in functions
• The spread ("...") operator in function calls and array literals
• Classes (ES6 classes will be @struct by default. You can add @unrestricted to override that behavior. See the 'JSDoc Tag Reference' section of the Google JS style guide for information about the @struct annotation.)
• Computed properties and short properties in object literals.
• Method declarations in object literals (though the 'super' keyword will not work, currently)
• "for of" loops
• generator functions
• template strings
• Better unicode escapes in string literals (e.g. "\u{1F436}" == "🐶")

Transpilation of these features will be supported soon:

• destructuring assignment
• modules

Type Checking

Optimizations

Code Printer

In progress.