SmugMug Map

SmugMug Map

An ordered hash map data structure with an interface and behavior similar to (but not exactly the same as) ECMAScript 6 Maps.


  • Efficient key/value data structure that maintains insertion order.

  • Use any JavaScript value (including objects, arrays, functions, NaN, even DOM elements) as keys.

  • Iterate over the map using each(), retrieve an array of entries with entries(), retrieve an array of keys with keys(), or retrieve an array of values with values().

  • O(1) lookup time for string keys. O(n) lookup time for other key types.

  • Set the objectIdName property to the name of a property to use as a unique id string for object keys, enabling much faster O(1) lookups for object keys that already have meaningful unique ids.

  • Or enable the autoStamp option to automatically stamp object keys with unique ids, enabling much faster O(1) lookups for object keys with no effort on your part.


Note: gallery-sm-map isn’t yet available on the Y! CDN, but feel free to grab it from this git repo!

Run this example!

YUI().use('gallery-sm-map', function (Y) {
    var map = new Y.Map();

    // String keys are super efficient.
    map.set('foo', 'bar');
    console.log(map.get('foo')); // => 'bar'

    // ...but object keys can be super convenient.
    var object = {};
    map.set(object, 'my key is an object!');
    console.log(map.get(object)); // => 'my key is an object!'

    // Even NaN can be a key!
    map.set(NaN, 'my key is not a number!');
    console.log(map.get(NaN)); // => 'my key is not a number!'

    // Iteration is easy.
    map.each(function (value, key) {
        // ...

Differences from ES6 Maps

  • delete() and remove() are equivalent for backwards compatibility with browsers that don’t support reserved words as property names (in ES6, only delete() is defined).

  • each() and forEach() are equivalent (in ES6, only forEach() is defined).

  • each() and forEach() are chainable.

  • each() will halt iteration if the callback returns false.

  • get() supports an optional defaultValue argument that will be returned if the given key isn’t found.

  • merge() merges one or more maps. There is no ES6 equivalent.

  • toJSON() is an alias for entries() (ES6 doesn’t define toJSON()).

  • Does not support ES6 iterators, as most browsers don’t implement them yet.

  • The Y.Map constructor accepts either an array of entries, a Y.Map instance, or a native Map instance containing entries that should be added to the new map. The ES6 Map constructor only accepts an array of entries.

  • The Y.Map constructor doesn’t accept a comparator argument, whereas the ES6 Map constructor does. Its only valid value in ES6 is the string “is”, which causes an ES6 Map to treat 0 and -0 as distinct values. If you care about this for some reason, I’d love to know why.

  • The Y.Map constructor accepts an options argument. The ES6 Map constructor does not.

  • In older browsers (notably IE8 and lower), the size property is enumerable and writable. This is unavoidable due to limitations in these browsers.

  • In older browsers that don’t support Object.create() (IE8 and lower), string keys with names that conflict with property names on Object.prototype will have O(n) lookup times.

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