https://github.com/component/symbol

ES6 symbols in ES5
https://github.com/component/symbol

Last synced: 13 days ago
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ES6 symbols in ES5

• Host: GitHub
• URL: https://github.com/component/symbol
• Owner: component
• Created: 2014-01-29T19:34:58.000Z (almost 11 years ago)
• Default Branch: master
• Last Pushed: 2015-03-23T06:33:50.000Z (almost 10 years ago)
• Last Synced: 2024-05-08T17:06:38.415Z (8 months ago)
• Language: JavaScript
• Homepage:
• Size: 143 KB
• Stars: 11
• Watchers: 15
• Forks: 4
• Open Issues: 0
• Metadata Files:
  • Readme: Readme.md
  • Changelog: History.md

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README

        
# symbol

  This component implements ECMAScript 6-like `Symbol`s in ECMAScript 5. 

  A `Symbol` can be used as a unique key for setting non-enumerable (i.e. "invisible") properties on objects.

  This is specially useful for implementing truly private stores in JS objects. This component can be used

  both on its own or as a Polyfill for ES6 `Symbol`s.

    var symbol = require('symbol');

    var obj = { name: 'John Doe' };

    (function() {

      var privateStore = symbol();

      obj[privateStore] = {

        secretAgent: true,

        realName: 'James Bond'

      }

    })();

    // this will not expose privateStore

    for (var key in obj) {

      console.log(key);

    }

## Installation

  Install with [component(1)](http://component.io):

    $ component install component/symbol

## API

### symbol()

Creates a new symbol.

### Symbol#dispose()

Disposes the symbol, releasing the global resources used by it.

This is only really needed when using a large number of short-lived, disposable `Symbol` objects.

Please refer to the *"Implementation Considerations"* and *"Memory Leak"* sections below for more details.

## Usage as a polyfill for native Symbols

    if (typeof window.Symbol == 'undefined') {

      window.Symbol = require('symbol');

    }

## Implementation Considerations

The implementation is based on an example on the WebReflection blog, by Andrea Giammarchi:

http://webreflection.blogspot.com/2013/03/simulating-es6-symbols-in-es5.html

(The original example implementation is MIT licensed, and so is this component.)

The "trick" for getting a non-enumerable property when using a `Symbol` as a key — without

having to manually resort to Object.defineProperty() every time — is defining for each symbol

a property on the global `Object` prototype, that's responsible for calling Object.defineProperty()

for us when set. This is not as bad as it sounds, as the property is both unique (using https://github.com/component/uid)

and non-enumerable.

### Memory Leak

**Important:** While collisions or changes in behavior will not be triggered by the presence of the

global property for the reasons stated above, its value will not be automatically released, so this specific 

implementation will by default leak memory over time if used for a very large number of disposable `Symbol` objects.

If you need to use a large number of disposable `Symbol` objects, make sure to manually call the `dispose()` method

on each of them before disposing them.

## License

  The MIT License (MIT)

  Copyright (c) 2013 WebReflection / Andrea Giammarchi

  Copyright (c) 2014 Automattic, Inc.

  Permission is hereby granted, free of charge, to any person obtaining a copy

  of this software and associated documentation files (the "Software"), to deal

  in the Software without restriction, including without limitation the rights

  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

  copies of the Software, and to permit persons to whom the Software is

  furnished to do so, subject to the following conditions:

  The above copyright notice and this permission notice shall be included in

  all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

  THE SOFTWARE.