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    This is an experimental technology, part of the ECMAScript 6 (Harmony) proposal.
    Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future version of browsers as the spec changes.


    The size accessor property returns the number of elements in a Map object.


    The value of size is an integer representing how many entries the Map object has. A set accessor function for size is undefined; you can not change this property.


    Example: Using size

    var myMap = new Map();
    myMap.set("a", "alpha");
    myMap.set("b", "beta");
    myMap.set("g", "gamma");
    myMap.size // 3


    Specification Status Comment
    ECMAScript 6 (ECMA-262)
    The definition of 'Map.prototype.size' in that specification.
    Release Candidate Initial definition.

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support 38 19 (19) 11 25 7.1
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support Not supported 38 19.0 (19) Not supported Not supported iOS 8

    Gecko-specific notes

    • From Gecko 13 (Firefox 13 / Thunderbird 13 / SeaMonkey 2.10) to Gecko 18 (Firefox 18 / Thunderbird 18 / SeaMonkey 2.15 / Firefox OS 1.0.1 / Firefox OS 1.1) the size property was implemented as a Map.prototype.size() method, this has been changed to a property in later versions conform to the ECMAScript 6 specification (bug 807001).

    See also

    Document Tags and Contributors

    Contributors to this page: realityking, fscholz
    Last updated by: realityking,