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    <p>jQuery's <code>extend</code> method allows you to simply copy object properties from one to another.</p> <p>Here's a contrived, but illustrative example. It even shows why you would not need to "deep" copy functions!</p> <pre><code>var someObj = { a : "a", b : 12345, c : { d : "d", e : "e" }, f : function() { alert(this.a); } }; //copy from original to new empty object var deepCopy = $.extend(true, {}, someObj); deepCopy.a = "deepCopy.a"; deepCopy.c.d = "deepCopy.c.d"; alert("someObj is not affected when deep copying: " + someObj.c.d); alert("deepCopy is entirely distinct when deep copying: " + deepCopy.c.d); deepCopy.f(); someObj.f(); </code></pre> <p>Here's a fiddle for your convenience: <a href="http://jsfiddle.net/S6p3F/3/">http://jsfiddle.net/S6p3F/3/</a></p> <p>Running this code you will see that <code>someObj</code> and <code>deepCopy</code> are identical in structure but distinct objects. </p> <p>As you can see, deep copying of functions is not required as the <code>this</code> reference is bound to whatever object the function is applied to. This is becausein javascript, calling a function as <code>deepCopy.f()</code> is functionally equivalent to <code>deepCopy.f.call(deepCopy)</code>. A more illustrative example:</p> <pre><code>function someFunction() { alert(this.someProperty); } var a = { someProperty: "a's property" }, b = { someProperty: "b's property" }; someFunction.call(a); someFunction.call(b); </code></pre> <p>And a fiddle: <a href="http://jsfiddle.net/S6p3F/2/">http://jsfiddle.net/S6p3F/2/</a></p>
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    1. COif you supply `true` as a first param to `extend` it does indeed do a deep copy. Example updated to reflect this. As for closures etc. anyone with a reasonable understanding of JS will understand this. My point was not that it would work in all circumstances, but that copying the function reference is usually all that is needed.
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    2. COI've commented on some other answer before about jQuery's extend. jQuery does some testing to see what kind of object an object is before it copies it. I have some significant doubts about this answer. Go ahead, search the jQuery source for this line: `if ( deep && copy && ( jQuery.isPlainObject(copy) || (copyIsArray = jQuery.isArray(copy)) ) ) {`
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    3. COHow do you intend to handle cloning an array or backbone collection? Shallow copy (extend) just changes the base reference, but not the references of the array elements.
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