Question

185

Javascript copy array to new array

rated 0 times [ 189] [ 4] / answers: 1 / hits: 87929 / 11 Years ago, sat, march 30, 2013, 12:00:00

I want to form an array from an existing array so I can modify the new array without affecting the old. I realise arrays are mutable and this is why the new array affects the old.

E.g.

old = [Apples, Bananas];

new = old;



new.reverse();

Old has also been reversed.

In Python, I can just do new = list(old), but doing new = new Array(old); puts the old list inside a list.

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monetm

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answered 11 Years ago katelynn · Accepted Answer

You can use the .slice method:

var old = [Apples, Bananas];

var newArr = old.slice(0);

newArr.reverse(); 

// now newArr is [Bananas, Apples] and old is [Apples, Bananas]

Array.prototype.slice returns a shallow copy of a portion of an array. Giving it 0 as the first parameter means you are returning a copy of all the elements (starting at index 0 that is)