johnjbarton / harmony-reflect

ES-Harmony reflect module shim

This is a shim for the ECMAScript 6 reflection module.

In a browser, after loading

<script src="reflect.js"></script>

a global object Reflect is defined that contains the functions from the ES6 reflect module (see below).

The Proxy object is also updated to follow the latest direct proxies spec. To create such a proxy, call:

var proxy = new Proxy(target, handler)

If you are using node.js (>= v0.7.8), you can install via npm:

npm install harmony-reflect

Then:

node --harmony
> require('harmony-reflect');

API

This module exports a single object named Reflect.

The ECMAScript 6 Proxy API allows one to intercept various operations on Javascript objects.

• Overview of all supported traps on proxies
• The Reflect API
• The Proxy Handler API

Compatibility

The Reflect API, with support for proxies, was tested on:

• Firefox 12 (should work since Firefox 4)
• Chrome 19, with the following flag enabled: chrome://flags/#enable-javascript-harmony (copy/paste into your address-bar)
• node --harmony (in node v0.7.8)
• v8 --harmony (on 3.11.0, should work since at least v3.6)
• spidermonkey shell

Dependencies

• ECMAScript 5/strict
• To emulate direct proxies: * old Harmony Proxies * Harmony WeakMaps

After loading reflect.js into your page or other JS environment, be aware that the following globals are patched to be able to recognize emulated direct proxies:

Object.{freeze,seal,preventExtensions}
Object.{isFrozen,isSealed,isExtensible}
Object.getPrototypeOf
Object.prototype.valueOf
Object.getOwnPropertyDescriptor
Object.defineProperty
Function.prototype.toString
Date.prototype.toString
Array.isArray
Array.prototype.concat
Proxy

Examples

The examples directory contains a number of examples demonstrating the use of proxies:

• membranes: wrappers that transitively isolate two object-graphs.
• observer: a self-hosted implementation of the ES7 Object.observe notification mechanism.
• profiler: a simple profiler to collect usage statistics of an object.

Other example uses of proxies (not done by me, but using this library):

• supporting negative array indices a la Python
• tpyo: using proxies to correct typo's in JS property names

Proxy Handler API

The sister project proxy-handlers defines a number of predefined Proxy handlers as "abstract classes" that your code can "subclass" The goal is to minimize the number of traps that your proxy handlers must implement.

Spec Compatibility

This library differs from the draft ECMAScript 6 spec. as follows:

• In ES6, Proxy will be a constructor function that will require the use of new. That is, you must write new Proxy(target, handler). This library exports Proxy as an ordinary function which may be called without using the new operator.
• Array.isArray(obj) and [].concat(obj) are patched so they work transparently on proxies-for-arrays (e.g. when obj is new Proxy([],{})). It is as yet unclear how ES6 will spec these operations in the presence of proxies.