Question

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What is the most efficient way to clone a JavaScript object?

I need to copy an (ordered, not associative) array of objects. I’m using jQuery. I initially tried

jquery.extend({}, myArray)

but, naturally, this gives me back an object, where I need an array (really love jquery.extend, by the way).

So, what’s the best way to copy an array?

Answer 1

Since Array.slice() does not do deep copying, it is not suitable for multidimensional arrays:

var a =[[1], [2], [3]];
var b = a.slice();

b.shift().shift();
// a is now [[], [2], [3]]

Note that although I’ve used shift().shift() above, the point is just that b[0][0] contains a pointer to a[0][0] rather than a value.

Likewise delete(b[0][0]) also causes a[0][0] to be deleted and b[0][0]=99 also changes the value of a[0][0] to 99.

jQuery’s extend method does perform a deep copy when a true value is passed as the initial argument:

var a =[[1], [2], [3]];
var b = $.extend(true, [], a);

b.shift().shift();
// a is still [[1], [2], [3]]