Updating Javascript Objects

Question

I have the following object:

var obj1 = {};

obj1.obj2 = {
  prop1: 0
};

and the following function:

function func1() {
    var p = obj1.obj2.prop1;
    p += 2;
    return p;
 };

When updating 'p' it has not updated 'obj1.obj2.prop1'. Instead of 'p' pointing to the original object is it now it's own object by itself? If so how can I make 'p' a pointer?

This answer may help: http://stackoverflow.com/a/7744623/1618257 — David Starkey, May 20 '13 at 18:57

score 4 · Accepted Answer · answered May 20 '13 at 19:04

When you do var p = obj1.obj2.prop1;, you are setting p to the value of prop1. So, when you update p, you're just updating the value set in p.

What you can do is set p to obj1.obj2. Then you can update p.prop1 and it should update obj1.

function func1() {
    var p = obj1.obj2;
    p.prop1 += 2;
    return p.prop1;
}

score 1 · Answer 2 · answered May 20 '13 at 19:03

1

Javascript doesn't have pass-by-reference so you would have to do the following:

var obj1 = {};

obj1.obj2 = {
    prop1: 0
};

function func1(obj) {
    obj.obj2.prop1 += 2;
    return obj.obj2.prop1;
};

func1(obj1);

answered May 20 '13 at 19:03

chrislondon

12,487
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26
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score 1 · Answer 3 · answered May 20 '13 at 19:03

1

p += 2 is just assigning an other number to p, this isn't modifying the object pointed to by p.

Do this instead:

obj1.obj2.prop1 += 2;

or

var obj = obj1.obj2;
obj.prop1 += 2;

answered May 20 '13 at 19:03

Arnaud Le Blanc

98,321
23
206
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Updating Javascript Objects

3 Answers3