weakmap-polyfill's Introduction

weakmap-polyfill

Installation

npm

$ npm install --save weakmap-polyfill

Usage

Import or require weakmap-polyfill, then WeakMap will be defined in the global scope if native WeakMap is not supported in running environment.

using `import`

import 'weakmap-polyfill';
const weakMap = new WeakMap();

using `require`

require('weakmap-polyfill');
var weakMap = new WeakMap();

browser (standalone)

<script src="weakmap-polyfill.min.js"></script>
<script>
var weakMap = new WeakMap();
</script>

Compatibility

Chrome 15
Firefox 3
IE 7
Safari 4
Opera 11.5
Edge

Browser Tests

Limitations

This polyfill has following few limitations.

WeakMap iterable argument is not supported. (23.3.1.1 WeakMap ( [ iterable ] ))
Frozen and sealed objects are not supported.
The values held by a WeakMap can't be collected once the map itself is GCed, since the values here are tied to the keys. #4

License

MIT

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weakmap-polyfill's Issues

Good work: Opera 12 eats it

Opera 12.17 Build 1863 Platform x64 System Windows 10 works with MutationObserver.js now.

Documenting limitations (frozen and sealed objects, values that outlive the WeakMap)

The approach taken by this lib is pretty good, since the GC lifetime of values is tied to that of keys, however, it has a few limitations that may be worth documenting:

The lib doesn't work with frozen and sealed objects.
The values held by a WeakMap can't be collected once the map itself is GCed, since the values here are tied to the keys.

A third thing, which is more of a suggestion:

Even if they are not enumerable, the keys can be obtained in some IE versions by using Object.getOwnPropertyNames. This could be mitigated relatively cheaply by storing the mapping inside a single object that is tied to the key object using a secret field as a value. You can then monkeypatch Object.getOwnPropertyNames to strip that secret field from the results and, also monkeypatch Object.getOwnPropertyNames if present (in IE thanks to a polyfill, not sure about other envs).

If this monkeypatch approach seems workable to you, you could also solve 1) by monkeypatching Object.freeze and Object.seal to add the secret field before freezing.

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