javascript what happens on array push?

Question

so I have:

var something = function () { return 6}

var foo = new something();

var arr = []
var arr2 = []

I do arr2.push(foo) and arr.push(foo)

What happens in the background? Is foo duplicated and put in 2 places? Is foo just foo and what's inside the arrays a reference to foo?

Thanks.

meder omuraliev · Accepted Answer · 2011-04-02 16:42:54Z

7

EDIT: I misread. Because you are invoking the function with new you create a new object. Any object is passed by reference.

var something = function () { return 6}

var foo = new something();

typeof foo is an object so in this case it is passed by reference.

~~Pretty sure that foo is duplicated since it's a primitive and not an object.~~

answered Apr 2, 2011 at 16:26

meder omuraliev

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2 Comments

Thanks, what if it were an object?

A reference to the object would be passed.

6502 · Accepted Answer · 2011-04-02 16:39:59Z

1

What's inside the arrays are references to the same instance of something. This can be checked easily using for example chrome javascript console...

enter image description here

As you can see adding a new member x to arr1[0] got it appearing on arr2[0].

answered Apr 2, 2011 at 16:39

6502

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