Equality in javascript objects?

Question

If I have this code:

var foo1 = new Foo();
var foo2 = new Foo();

and I want to do this:

function updateFoo1 (foo) 
{
   if (foo === foo1) //If foo is foo1
   {
       //code for processing
       return true;
   }
   else //Foo must be foo2 or another instance of foo not foo1
     return false;
}

Will this work as expected to make sure whether the function argument foo is the same as foo1 and not foo2 or any other instance of the foo class? If not, what should I do to get the result I want?

If you're testing that they're the same instance, then yes it works. Didn't it work when you tried it? — user1106925
– user1106925, Commented Apr 28, 2012 at 19:35
I don't know why people upvote questions like this. A 12k user should know to do basic research and testing before asking such a question. — user1106925
– user1106925, Commented Apr 28, 2012 at 19:58
@amnotiam If you don't want to answer a question, then don't. Simple. The question I asked is perfectly within the rules of this site to ask, and asking a question here always gives better results than googling something. Simply ignore questions that you don't like rather than trolling them. — Ali
– Ali, Commented Apr 29, 2012 at 0:15
Please review the how to ask section, specifically under the Do your homework heading. You should know how the site works after asking over 460 questions. I mean seriously. Posting some code and basically asking someone else to test its result is poor. — user1106925
– user1106925, Commented Apr 29, 2012 at 1:06

The Alpha · Accepted Answer · 2012-04-28 19:50:12Z

2

function Foo(){}
var foo1 = new Foo();
var foo2 = new Foo();
console.log(foo1===foo2); // always false

Object comparison is being done by object's reference so foo1 returns a different reference and foo2 returns another reference. In your case

function updateFoo1(foo) 
{
    if (foo === foo1)
    {
        //code for processing
        return true;
    }
    else return false;
}
updateFoo1(foo1) // first if condition will work and will return true
updateFoo1(foo2) // else condition will work and will return false

See yourself here.

answered Apr 28, 2012 at 19:50

The Alpha

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