how to pass by reference in javascript

Question

How should I pass by reference in a JavaScript function?

For example:

function passByReference(a){
    a = "banana";
}

var x = "apple";
passByReference(x);

Here x should output banana.

I am new to JavaScript; any help would be appreciated. Thanks in advance.

Gabriel · Answer 1 · 2014-05-02T19:38:28.163

2

Wrap the variable with an object. Properties of objects are passed by reference.

function passByReference(a) {
   a.fruit = 'banana';
}

var wrapper = {fruit: 'apple'};
passByReference(wrapper);

edited May 02 '14 at 19:38

answered May 02 '14 at 06:51

Gabriel

862
6
18

1

Not exactly. Objects are also passed by value. However the properties are references itself. For example: This would not work `a={fruit: 'banana'}` inside the function – Zhonk May 02 '14 at 06:57
yeah @zhonk you are right properties are references itself and objects are also passed by value. – azero0 May 02 '14 at 07:33

score 0 · Accepted Answer · answered May 02 '14 at 07:01

You cannot pass by reference. If you want to modify the state of your caller from within the called function, there are two ways you could do:

Sometimes it fits best to wrap the state in an object:

var x = { valueToChange: 'initialValue' };
passByReference(x);

This works because with objects, a pointer to the address where the object lies is passed. That pointer is passed by value but it still points to the same object.

In some other cases a callback does the trick:

var x = "apple";

passByReference(function (newValue) { x = newValue; });

function passByReference(callback) {
    callback("banana");
}

This works because if you define a function as above it builds a closure together with all variables it references. When your function gets called it really modifies the value of x.

how to pass by reference in javascript

2 Answers2