author: Krasimir Tsonev

Hi there, I'm . Senior front-end engineer with over 13 years of experience. I write, speak and occasionally code stuff. Follow me on Twitter, GitHub, Facebook or LinkedIn

JavaScript: dependency free extend method

While I worked on AbsurdJS I needed a function which accepts numerous objects and combines their properties. I.e. something like the _.extend method of UnderscoreJS. What I did is actually to use one more dependency just because of such method. John-David Dalton nicely pointed out my mistake and added a simple function which solved the problem. I change it a bit and now it acts as UnderscoreJS's version.

var extend = function() {   
    var process = function(destination, source) {   
        for (var key in source) {
            if (, key)) {
                destination[key] = source[key];
        return destination;
    var result = arguments[0];
    for(var i=1; i<arguments.length; i++) {
        result = process(result, arguments[i]);
    return result;

Here is a short Jasmine test:

describe("Testing utils /", function() {

    it("should use extend", function(done) {
        var o = {prop: 10};
        o = extend(o, { prop: 20 }, { prop: 30, name: "Extend" }, { prop: 40, address: "Bla Bla" });


The resulted o object has the following value:

    prop: 40, 
    name: "Extend", 
    address: "Bla Bla"
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