Node/Javascript setting object property to array not working?

Question

var arr = new Array();
arr[0] = "a";
var ob = new Object();
ob.prop = arr;
ob.prop[0] = "b";
//Console log arr[0] returns b

for some reason, the arr array is being changed when I change ob.prop ?

What am I missing?

You've assigned a reference to the same Array. – the system Mar 13 '13 at 23:15 — the system, Mar 13 '13 at 23:15

score 1 · Answer 1 · edited May 23 '17 at 12:04

1

As the system pointed out, ob.prop = arr is basically just giving another name for accessing the object referenced by arr. So when you modify ob.prop you are modifying the same object that arr also refers to.

EDIT: For copying an array take a look at this question:

var arrCopy = arr.slice();

edited May 23 '17 at 12:04

Community

1
1

answered Mar 13 '13 at 23:27

Jorge Israel Peña

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So how would I go about creating a copy of arr instead of a reference to it? – user2123244 Mar 13 '13 at 23:32

score 1 · Answer 2 · answered Mar 13 '13 at 23:37

As Jorge mentioned, this is happening because obj.prop is just a reference to arr, so arr and obj.prop will point to the same place in memory. So if you change either, the value in memory (which the other is pointing to) changes, thus changing both.

If you're looking to avoid this you need to do a deep copy. This will copy the values of the array into a new array, which obj.prop will point at.

There is a walk-through of how to do this in javascript here.

Node/Javascript setting object property to array not working?

2 Answers2