using splice(0) to duplicate arrays

Question

I have two arrays: ArrayA and ArrayB. I need to copy ArrayA into ArrayB (as opposed to create a reference) and I've been using .splice(0) but I noticed that it seems to removes the elements from the initial array.

In the console, when I run this code:

var ArrayA = [];
var ArrayB = [];

ArrayA.push(1);
ArrayA.push(2);

ArrayB = ArrayA.splice(0);

alert(ArrayA.length);

the alert shows 0. What am I doing wrong with .splice(0)??

Thanks for your insight.

@sp00m: I like PascalNotation; I just think it looks better. — frenchie
– frenchie, Commented Aug 22, 2012 at 12:32
@frenchie I'm talking about conventions. PascaleNotation is reserved for classes, whereas lowerCamelCase is used for methods/functions and variables/attributes/properties. — sp00m
– sp00m, Commented Aug 22, 2012 at 12:34
@sp00m: I know about conventions but I really do prefer the looks of PascalNotation. — frenchie
– frenchie, Commented Aug 22, 2012 at 12:50

Sirko · Accepted Answer · 2012-08-22 12:28:54Z

54

You want to use slice() (MDN docu) and not splice() (MDN docu)!

ArrayB = ArrayA.slice(0);

slice() leaves the original array untouched and just creates a copy.

splice() on the other hand just modifies the original array by inserting or deleting elements.

answered Aug 22, 2012 at 12:28

Sirko

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Imp · Accepted Answer · 2012-08-22 12:30:18Z

7

splice(0) grabs all the items from 0 onwards (i.e. until the last one, i.e. all of them), removes them from the original array and returns them.

answered Aug 22, 2012 at 12:30

Imp

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KooiInc · Accepted Answer · 2012-08-22 12:32:09Z

5

You are looking for slice:

var a = [1,2,3,4,5]
   ,b = a.slice();
//=> a = [1,2,3,4,5], b = [1,2,3,4,5]

you can use splice, but it will destroy your original array:

var a = [1,2,3,4,5]
   ,b = a.splice(0);
//=> a = [], b = [1,2,3,4,5]

answered Aug 22, 2012 at 12:32

KooiInc

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