es6-shim – ECMAScript 6 functionality on ECMAScript 5

Update 2012-03-13: Added a section on installation.

Paul Miller’s es6-shim gives you functionality that will be in ECMAScript 6 (code-named ECMAScript.next), on ECMAScript 5 engines. It was initially based on a project of mine, but adds much new functionality, Node.js compatibility, and (not least) tests.

Highlights

The following are a few highlights. Take a look at the tests to get more usage examples.

• Strings

      > "hello world".startsWith("hello")
      true
      > "hi".repeat(3)
      'hihihi'
  

• Object.getOwnPropertyDescriptors() – makes Object.create() more useful.

      var copy = Object.create(Object.getPrototypeOf(orig),
          Object.getOwnPropertyDescriptors(orig));
  
      var newFoo = Object.create(FooProto,
          Object.getOwnPropertyDescriptors({
              instanceProp1: 123,
              instanceProp2: "abc"
          }));
  

• Object.is() – an improved version of === (which will likely become an operator called is in ECMAScript 6).

      > 0 === -0
      true
      > Object.is(0, -0)
      false
      > NaN === NaN
      false
      > Object.is(NaN, NaN)
      true
  

• Map – gives you a dictionary with arbitrary keys.

      > var m = new Map();
      undefined
      > m.set("1", "foo");
      undefined
      > m.set(1, "bar");
      undefined
      > m.get("1")
      'foo'
      > m.get(1)
      'bar'
  

  "1" and 1 are (coerced to) the same key with arrays. Note that each object is considered different from any other object. Hence, the following map entry cannot be easily retrieved:

      > m.set({}, "hello");
      > m.get({})  // new object!
      undefined
  

Installation

You can either load es6-shim.js as a script in a browser or install it via npm on Node.js (requires at least version 0.6.5):

    npm install es6-shim

Afterwards, you enable it in your project like this:

    require("es6-shim");

And you can play with it on the Node.js REPL, with the option of enabling it by default [2].

Related posts

1. ECMAScript.next: the “TXJS” update by Eich [what will be in ECMAScript 6, code-named ECMAScript.next]
2. Execute code each time the Node.js REPL starts