for vs forEach

JavaScript performance comparison

Revision 57 of this test case created by Gajus

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>
  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;
    };
    
    function each1 (data, iterator) {
        var i,
                length = data.length;
        for (i = 0; i < length; i += 1) {
                iterator(data[i], i, data);
        }
    }
    
    function each2 (data, iterator) {
        var i,
                length = data.length;
        for (i = 0; i < length; ++i) {
                iterator(data[i], i, data);
        }
    }
  };

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

Test runner

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Testing in unknown unknown
Test Ops/sec
strict 0 comparison
 
var arr = values,
    length = arr.length;
while (length-- !== 0) {
    add(arr[length], length, arr);
}
 pending…
for loop, cached length, callback
 
var arr = values,
    length = arr.length + 1;
while (--length !== 0) {
    add(arr[length-1], length-1, arr);
}
 pending…
for loop, cached length, callback, reduce op
 
var arr = values,
    length = arr.length;
for (var i = 0; i < length; ++i) {
    add(arr[i], i, arr);
}
 pending…
new each
 
each(values, add);
 pending…
without strict zero comparison
 
var arr = values,
    length = arr.length;
while (length--) {
    add(arr[length], length, arr);
}
 pending…
each1
 
each1(values, add);
 pending…
each2
 
each2(values, add);
 pending…

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