A forward polyfill for ES6 Maps

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Use ES6 Maps with a bunch of convenience methods. Help improve the ES6 spec!

var map = new Map();
map.set('foo', 'bar');
map.set(0, 42);

// Filter map by a function
map.filter(function(key, value) {
   return typeof key == 'string';
=> new Map([[0, 42]])

// Merge Maps
map.merge(new Map([['baz', 'thing']]));
=> new Map([[0, 42], ['baz', 'thing']])

// map.get with a default
map.fetch('NON_EXISTANT', 'default');
=> 'default'

// Invert map (makes keys->values and vice versa)
=> new Map([[42, 0], ['thing', 'baz']])

// Destructive filter (inline map delete)
map.reject(function(key, value) {
  return typeof key == 'string';
=> false

// Remove all items

// Check if Map has no items
=> true


You can install this via npm for node.js v0.8+

npm install smap

For browsers, just include smap.js in your page.

Environment Support

If you also use the es5-shim, you can use this in:

  • IE7+
  • Firefox 4+
  • Google Chrome 21+
  • Safari 4+
  • Opera 12+
  • Node.js 0.8+
  • PhantomJS

Why this project exists

Boris Smus makes an excellent suggestion for moving the web forward: forward polyfills. I hope this project can be the basis for a future proposal to TC39. Please gratuitously discuss Map and WeakMap workings in issues, and add methods/tests with pull requests.

This is for everyone, not just JavaScript gurus. Standards bodies want feedback from developers like you.