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POJavascript by reference vs. by value
 

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    <p>I'm looking for some good comprehensive reading material on when Javascript passes something by value and when by reference and when modifying a passed item affects the value outside a function and when not. I'm also interested in when assigning to another variable is by reference vs. by value and whether that follows any different rules than passing as a function parameter.</p> <p>I've done a lot of searching and find lots of specific examples (many of them here on SO) from which I can start to piece together pieces of the real rules, but I haven't yet found a single, well written document that describes it all.</p> <p>Also, are there ways in the language to control whether something is passed by reference or by value?</p> <p>Here are some of the types of questions I want to understand. These are just examples - I'm actually looking to understand the rules the language goes by, not just the answers to specific examples. But, here are some examples:</p> <pre><code>function f(a,b,c) { a = 3; b.push("foo"); c.first = false; } var x = 4; var y = ["eeny", "miny", "mo"]; var z = {first: true}; f(x,y,z); </code></pre> <p>When are the contents of x, y and z changed outside the scope of f for all the different types?</p> <pre><code>function f() { var a = ["1", "2", "3"]; var b = a[1]; a[1] = "4"; // what is the value of b now for all possible data types that the array in "a" might hold? } function f() { var a = [{yellow: "blue"}, {red: "cyan"}, {green: "magenta"}]; var b = a[1]; a[1].red = "tan"; // what is the value of b now and why? b.red = "black"; // did the value of a[1].red change when I assigned to b.red? } </code></pre> <p>If I want to make a fully independent copy of an object (no references whatsoever), what's the best practice way to do that?</p>
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    1. COThis is a worthwhile read: [Wiki: Evaluation Strategy](http://en.wikipedia.org/wiki/Evaluation_strategy). I prefer Call By Object Sharing to avoid such confusion and leave Call By Reference to actually mean something else, where it applies. To make a "clone" consider `jQuery.extend` (shallow clone only!) or similar provided by your choice of framework. (I think ECMA ed. 5 introduces `Object.clone` ...?). A "deep clone" can be achieved with serializing to JSON and back, where such an operation is preserving (it might not always be). I am sure there are also other functions designed for this :)
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