Object.is

Summary

Determines whether two values are the same value.

Syntax

var isSame = Object.is(value1, value2);

Parameters

value1

The first value to compare.

value2

The second value to compare.

Description

Object.is() determines whether two values are the same value.  Two values are the same if one of the following holds:

• both undefined
• both null
• both true or both false
• both strings of the same length with the same characters
• both the same object
• both numbers and
  • both +0
  • both -0
  • both NaN
  • or both non-zero and both not NaN and both have the same value

This is not the same as being equal according to the == operator.  The == operator applies various coercions to both sides before testing for equality (resulting in such behavior as "" == false being true), but Object.is doesn't coerce either value.

This is also not the same as being equal according to the === operator.  The === operator (and the == operator as well) treats the number values -0 and +0 as equal, and it treats NaN as not equal to NaN.

Compatibility

Object.is is a proposed addition to the ECMA-262 standard; as such it may not be present in all browsers. You can work around this by utilizing the following code at the beginning of your scripts. This will allow you to use Object.is when there is still no native support.

if (!Object.is) {
  Object.is = function(v1, v2) {
    if (v1 === 0 && v2 === 0)
      return 1 / v1 === 1 / v2;
    if (v1 !== v1)
      return v2 !== v2;
    return v1 === v2;
  };
}

Examples

Object.is("foo", "foo");     // true
Object.is(window, window);   // true

Object.is("foo", "bar");     // false
Object.is([], []);           // false

var test = {a: 1};
Object.is(test, test)       // true

Object.is(null, null)       // true

// Special Cases
Object.is(0, -0);            // false
Object.is(-0, -0);           // true
Object.is(NaN, 0/0);         // true

Browser compatibility