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WeakMap collection as specified in ECMAScript6

Roughly inspired by Mark Miller's and Kris Kowal's WeakMap implementation.

Differences are:

  • Assumes compliant ES5 environment (no weird ES3 workarounds or hacks)
  • Well modularized CJS style
  • Based on one solution.


  • Will fail on non extensible objects provided as keys


$ npm install es6-weak-map

To port it to Browser or any other (non CJS) environment, use your favorite CJS bundler. No favorite yet? Try: Browserify, Webmake or Webpack


If you want to make sure your environment implements WeakMap, do:


If you'd like to use native version when it exists and fallback to polyfill if it doesn't, but without implementing WeakMap on global scope, do:

var WeakMap = require('es6-weak-map');

If you strictly want to use polyfill even if native WeakMap exists, do:

var WeakMap = require('es6-weak-map/polyfill');


Best is to refer to specification. Still if you want quick look, follow example:

var WeakMap = require('es6-weak-map');
var map = new WeakMap();
var obj = {};
map.set(obj, 'foo'); // map 
map.get(obj);        // 'foo' 
map.has(obj);        // true 
map.delete(obj);     // true 
map.get(obj);        // undefined 
map.has(obj);        // false 
map.set(obj, 'bar'); // map 
map.has(obj);        // false 

Tests Build Status

$ npm test