for vs forEach

JavaScript performance comparison

Revision 49 of this test case created by smith

Info

Is it faster to use the native forEach or just loop with for?

Inspired by Adrian Sutton's tests at: http://www.symphonious.net/2010/10/09/javascript-performance-for-vs-foreach/

This one adds random floating point numbers to see if the loop overhead is significant at all in the face of standard work.

Preparation code

<script src="http://code.jquery.com/jquery-1.8.2.min.js">
</script>
<script>
Benchmark.prototype.setup = function() {
    var i,
        value,
        length,
        values = [],
        sum = 0,
        context = values;
   
   
    for (i = 0; i < 10000; i++) {
        values[i] = Math.random();
    }
   
    function add(val) {
        sum += val;
    }
    function addEach(k, val) {
        sum += val;
    }
   
    var toString = Object.prototype.toString;
   
    function isArray(obj) {
        return toString.call(obj) === '[object Array]';
    }
   
    function isObject(obj) {
        return toString.call(obj) === '[object Object]';
    }
   
    function isString(obj) {
        return toString.call(obj) === '[object String]';
    }
   
    function each(obj, iterator) {
        var key, length;
        if (!obj) {
                return;
        }
        length = obj.length;
   
        if (isArray(obj) || isString(obj)) {
                for(key = 0; key < length; key += 1) {
                        iterator(obj[key], key, obj);
                }
                return obj;
        }
   
        if (isObject(obj)) {
                for(key in obj) {
                        if (obj.hasOwnProperty(key)) {
                                iterator(obj[key], key, obj);
                        }
                }
                return obj;
        }
   
        return obj;
    };
};

Benchmark.prototype.teardown = function() {
    i = 0;
    value = 0;
    length = 0;
    values = [];
    sum = 0;
};
</script>

Test runner

Warning! For accurate results, please disable Firebug before running the tests. (Why?)

Java applet disabled.

Testing in unknown unknown
Test Ops/sec
forEach
values.forEach(add);
pending…
for loop, cached length, callback
var arr = values,
    length = arr.length;
for (var i = 0; i < length; i++) {
    add(arr[i], i, arr);
}
pending…
for loop, cached length, callback.call
length = values.length;
for (i = 0; i < length; i++) {
    add.call(context, values[i], i, values);
}
pending…
$.each
$.each(values, addEach);
pending…
for loop, assignment condition, callback
for (i = 0; (value = values[i]) !== undefined; i++) {
    add(value, i, values);
}
pending…
for loop, assignment condition, callback.call
for (i = 0; (value = values[i]) !== undefined; i++) {
    add.call(context, value, i, values);
}
pending…
native map function
values.map(add);
pending…
new each
each(values, add);
pending…

Compare results of other browsers

Revisions

You can edit these tests or add even more tests to this page by appending /edit to the URL. Here’s a list of current revisions for this page:

0 comments

Add a comment