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Comparing jQuery and Underscore extend() functions for performance.

Preparation code

<script src="//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<script src="http://documentcloud.github.com/underscore/underscore-min.js"></script>
<script src="//sjhcockrell.s3.amazonaws.com/downloads/belt.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/lodash.js/1.0.0-rc.3/lodash.min.js"></script>
<script>
var lodash = _.noConflict();
</script>
<script>
  Benchmark.prototype.setup = function() {
    var targetObject,
        extendingObject,
        targetArray = [],
        extendingArray = [];
    
    
    //  Populate Arrays.
    for (var i = 0; i < 10000; i += 1) {
        targetArray[i] = i;
        extendingArray[i] = (i * 12) / 3;
    }
    
    targetObject = {
            a: [],
            b: {
                one: "one",
                two: {
                  point1: 2.1,
                  point2: 2.2,
                  point3: 2.3
                },
                three: [3.1, 3.2, 3.3, 3.4]
            },
            c: function(b) { b = 1; return b },
            d: "okay",
            e: 1
        };
    
    extendingObject = {
       prop: function(){ return "prop"; },
       d: targetArray,
       f: function getE() { this.e = this.e * 1000; return this.e; }
    };
    
    var objectTypes = {
        'boolean': false,
        'function': true,
        'object': true,
        'number': false,
        'string': false,
        'undefined': false
    };
    
    var X = {
        extend: function(object, source, guard) {
            var index,
                iteratee = object,
                result = object;
    
            if (!object) return result;
    
            var argsIndex = 1,
                argsLength = typeof guard == 'number' ? 2 : arguments.length;
    
            for (;argsIndex < argsLength; argsIndex++) {
                if ((iteratee = arguments[argsIndex])) {
                    var skipProto = typeof iteratee == 'function' && propertyIsEnumerable.call(iteratee, 'prototype');
    
                    var ownIndex = -1,
                        ownProps = objectTypes[typeof iteratee] ? nativeKeys(iteratee) : [],
                        length = ownProps.length;
    
                    while (++ownIndex < length) {
                        index = ownProps[ownIndex];
                        if (!(skipProto && index == 'prototype')) {
                            result[index] = iteratee[index]
                        }
                    }
                }
            }
    
            return result;
        }
    };
  };
</script>

Preparation code output

Test runner

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$.extend(targetObject, extendingObject);

B.extend(targetObject, extendingObject);

lodash.extend(targetObject, extendingObject);

// Cleaned up version of lodash.
X.extend(targetObject, extendingObject);

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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:

• Revision 1: published by John Cockrell on 2nd January 2013
• Revision 2: published by John Cockrell on 19th January 2013 and last updated on 20th January 2013
• Revision 3: published by John Cockrell on 22nd January 2013
• Revision 4: published by John Cockrell on 22nd January 2013
• Revision 5: published by John Cockrell on 22nd January 2013
• Revision 6: published by John Cockrell on 22nd January 2013

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