Dive Into JavaScript

JavaScript Array map

The JavaScript Array map method applies a callback function to every element of an array.

Syntax

array.map(callback [, contextObject])

Parameters

callback

The callback function to execute for each element

contextObject

Object to be used as a context for the callback function

Cross-browser Array map

For browsers that don't support the Array map method, here's an alternative implementation:

/**
 * Copyright (c) Mozilla Foundation http://www.mozilla.org/
 * This code is available under the terms of the MIT License
 */
if (!Array.prototype.map) {
    Array.prototype.map = function(fun /*, thisp*/) {
        var len = this.length >>> 0;
        if (typeof fun != "function") {
            throw new TypeError();
        }

        var res = new Array(len);
        var thisp = arguments[1];
        for (var i = 0; i < len; i++) {
            if (i in this) {
                res[i] = fun.call(thisp, this[i], i, this);
            }
        }

        return res;
    };
}

See also

• The JavaScript Array Object
• JavaScript Array every
• JavaScript Array filter
• JavaScript Array forEach
• JavaScript Array reduce
• JavaScript Array reduceRight
• JavaScript Array some