JavaScript Objects as argument to functions

Question

I am a little confused about the way JavaScript treats objects passed as arguments to functions.

For example, in the following code:

var a = {
  val: "old"
};
var b = {
  val: "old"
};

function update(a, b) {
  a.val = "new";
  b = {
    val: "new"
  };
}

update(a, b);

console.log(a, b);

The output comes as:

The val property of a is changed but that of b is not. I read somewhere that Objects are passed by reference to functions. Can anyone please explain this behaviour.

Thanks in advance.

score 0 · Answer 1 · answered May 02 '17 at 06:16

0

In the a case you are changing the object that variable a points to. In the b case you are creating a new object and making b points to this new object.

answered May 02 '17 at 06:16

Ankur

32,829
2
44
72

score 0 · Accepted Answer · edited May 02 '17 at 07:44

0

When you make this

function update(a, b) {
  a.val = "new";
  b = {
    val: "new"
  };
}

you are pointing b to a new object, but only in the update function

edited May 02 '17 at 07:44

iblamefish

4,631
3
32
44

answered May 02 '17 at 06:18

Ferus7

677
1
11
21

thanks. that cleared the confusion – Varun Sharma May 02 '17 at 06:26

score 0 · Answer 3 · answered May 02 '17 at 06:18

0

Actually the object references are passed by value to the function, And that is why when you changed the property of a it reflected. But as you assigned a new object to b, b inside the function got referenced to the new object.

answered May 02 '17 at 06:18

Jins Peter

2,147
1
16
33

JavaScript Objects as argument to functions

3 Answers3