This is a very old polyfill which served old browser decently for the last 4+ years. I am not actively maintaining this project but I would eventually accept PRs if you really need to use it.
Please have a look at better alternatives such ES-Shims
The aim of this repository is to provide an unobtrusive, performances oriented shim for ES6 collections such WeakMap, Map, and Set.
These global functions are already available in Firefox Nightly and Chrome Dev channel through Enable Experimental JavaScript in chrome://flags/ section.
- compatible with all browsers and both node.js (
npm install es6-collections) and Rhino - 100% unobtrusive with any environment. If implemented in node V8 it exports native constructors rather than shims
- size and performances oriented polyfill. It does not matter if the WeakMap is not perfect, it's just fast and not much more memory leaks prone than other shims. If you don't rely on magic, simply remember to
weakmap.delete(referedObject)when referedObject is not needed anymore. - for browsers, it fits in less than 1Kb once minzipped ... the smallest shim out there so far
- 100% of code coverage
- completely private shared behavior in order to easily maintain and update three collections at once
- API updated to the MDN docs
- tests are replaced with mocha and testling, which gets testling table and better testing possibilities
- polyfills for old browsers moved out to autopolyfiller
- used prototypical shared methods approach since it demonstrates times better results - test on jsperf
- removed both keys and values properties since these are not in specs anymore
- improved checks in order to do not fail with NaN or -0 and +0 as specified via specs
- native Array.prototype.indexOf used when key/value to retrieve is not NaN or -0 and +0 (performances regardless checks)
- updated tests including all methods behaviors plus
(Map|Set)#size()test for Mozilla only
- first of all, ES6 Collections is not about WeakMap only ... most likely is about Map ... anyway ...
- O(n) against O(1) to link keyObject and value is a no-go for different reasons:
- the random property attached to the object will be easily discoverable via for/in loop in all non ES5 capable engines, obtrusive
- even in ES5 capable browser, to make the random property not discoverable we need to wrap native Object.defineProperty, Object.defineProperties, Object.create, Object.getOwnPropertyNames, plus eventually Proxy, which means the whole application will be O(n) times slower for everything, not Map or WeakMap only
- there are situations where a random property cannot be attached, as example in Internet Explorer some object exposed in JavaScript may not accept runtime attached properties. The purpose of this shim is to be as cross platform as possible and as safe as possible while others polyfills are able to break, just as example, objects defined via VB Classes
- it's simply not possible to create 100% WeakMap in ES5 only, the aim of this polyfill is to bring a 1:1 unobtrusive and reliable API rather than 1:1 implementation
- if you think WeakMap, never existed until now, is the only thing you need, you may consider the first proposed alternative and simply walk away from this page
- a polyfill aim is to bring a reliable API until the browser supports it and you can simply remove the polyfill dependency. The perfect implementation may be unnecessary, in this case obtrusive, or simply YAGNI
- the bigger and rich in dependencies WeakMap shim from Mark S. Miller, the best attempt to avoid undesired memory leaks. Bear in mind some leak is still possible plus Object natives are wrapped plus it brings WeakMap only
- the unfortunately and so far slower and heavier, memory usage speaking, alternative from Benvie Harmony Collections Shim
- differently implemented Map and Set (no WeakMap) from Paul Millr, together with few others ES6 prototypes
- another attempt based on valueOf to avoid IE enumerability, still problematic with unknown objects but less leaks prone from Gozala
Just type $ mocha or $ npm test from the project’s folder in terminal.
$ npm build to build browser version of bundle.
es6-collections and the rest of the project is under Mit Style License
Copyright (C) 2011 by Andrea Giammarchi, @WebReflection
Permission is hereby granted, free of charge, to any person obtaining a copy
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in the Software without restriction, including without limitation the rights
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copies of the Software, and to permit persons to whom the Software is
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