Why Array.indexOf doesn't find identical looking objects

javascript arrays search object indexof
Jibla picture Jibla · Sep 26, 2012 · Viewed 43.7k times · Source

I have array with objects.

Something Like this:

var arr = new Array(
  {x:1, y:2},
  {x:3, y:4}
);

When I try:

arr.indexOf({x:1, y:2});

It returns -1.

If I have strings or numbers or other type of elements but object, then indexOf() works fine.

Does anyone know why and what should I do to search object elements in array?

Of course, I mean the ways except making string hash keys for objects and give it to array...

Answer

Selvakumar Arumugam picture Selvakumar Arumugam · Sep 26, 2012

indexOf compares searchElement to elements of the Array using strict equality (the same method used by the ===, or triple-equals, operator).

You cannot use === to check the equability of an object.

As @RobG pointed out

Note that by definition, two objects are never equal, even if they have exactly the same property names and values. objectA === objectB if and only if objectA and objectB reference the same object.

You can simply write a custom indexOf function to check the object.

function myIndexOf(o) {    
    for (var i = 0; i < arr.length; i++) {
        if (arr[i].x == o.x && arr[i].y == o.y) {
            return i;
        }
    }
    return -1;
}

DEMO: http://jsfiddle.net/zQtML/

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