Does javascript handle objects by reference or by value?

Question

I have this code

var myObjects = {}; //global variable

//Later on in the code:
for (i in myObjects)
{
    var obj = myObjects[i];
    process(obj);
}

function process(obj)
{
    $.getJSON("example.com/process/", {id: obj.id}, function(result)
      {
          //Will the following change the permanent/global copy e.g 
          // myObjects[44] ?
          obj.addItem(result.id, result.name, result.number);
      }
    );
}

Will the following line:

     obj.addItem(result.id, result.name, result.number);

modify the object by value or by reference, i.e will it modify the local copy of obj or e.g myObjects[44]?

If it affects only the local copy, how can I have it change the global copy of the object?

Daniel Vassallo · Accepted Answer · 2010-02-16 23:10:30Z

4

Primitive variables are passed by value in JavaScript, but objects are passed by reference.

Source and further reading:

JavaScript: Passing by Value or by Reference

edited Feb 16, 2010 at 23:10

answered Feb 15, 2010 at 16:20

Daniel Vassallo

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3 Comments

Pointy Over a year ago

Note that it's a little weirder than that: if you create a string by calling "new String('hi mom')" then it works kind-of like a string sometimes, but it'll act like an Object for parameter passing. That is, it's passed by reference.

Ruan Mendes Over a year ago

Actually, strings are immutable in js. Therefore, you are always passing them by reference. All operations on strings return a new string.

Andrew Over a year ago

In JavaScript, when you pass an object, you are really passing an object reference by value. See this earlier question.

Community · Accepted Answer · 2017-05-23 10:34:57Z

1

JavaScript is pass by value, as has been clarified in an earlier question. (Someone with more powers should mark this as duplicate--the answers here are incorrect.)

edited May 23, 2017 at 10:34

CommunityBot

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answered Dec 10, 2012 at 23:32

Andrew

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Comments

jellyfishtree · Accepted Answer · 2010-02-15 16:38:03Z

0

all non-object variables are pass-by-value afaik..

answered Feb 15, 2010 at 16:38

jellyfishtree

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