Object.is()

The Object.is() method determines whether two values are the same value.

Syntax

Object.is(value1, value2);

Parameters

value1: The first value to compare.
value2: The second value to compare.

Return value

A Boolean indicating whether or not the two arguments are the same value.

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 in the same order
both the same object (meaning both values reference the same object in memory)
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 (if they are not the same Type) 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 only difference between Object.is() and === is in their treatment of signed zeroes and NaNs. For example, the === operator (and the == operator) treats the number values -0 and +0 as equal. Also, the === operator treats Number.NaN and NaN as not equal.

Examples

Using Object.is

// Case 1: Evaluation result is the same as using ===
Object.is(25, 25);                // true
Object.is('foo', 'foo');          // true
Object.is('foo', 'bar');          // false
Object.is(null, null);            // true
Object.is(undefined, undefined);  // true
Object.is(window, window);        // true
Object.is([], []);                // false
var foo = { a: 1 };
var bar = { a: 1 };
Object.is(foo, foo);              // true
Object.is(foo, bar);              // false

// Case 2: Signed zero
Object.is(0, -0);                 // false
Object.is(+0, -0);                // false
Object.is(-0, -0);                // true
Object.is(0n, -0n);               // true

// Case 3: NaN
Object.is(NaN, 0/0);              // true
Object.is(NaN, Number.NaN)        // true

Polyfill

if (!Object.is) {
  Object.defineProperty(Object, "is", {
    value: function (x, y) {
      // SameValue algorithm
      if (x === y) {
        // return true if x and y are not 0, OR
        // if x and y are both 0 of the same sign.
        // This checks for cases 1 and 2 above.
        return x !== 0 || 1 / x === 1 / y;
      } else {
        // return true if both x AND y evaluate to NaN.
        // The only possibility for a variable to not be strictly equal to itself
        // is when that variable evaluates to NaN (example: Number.NaN, 0/0, NaN).
        // This checks for case 3.
        return x !== x && y !== y;
      }
    }
  });
}

Specifications

Specification
ECMAScript Language Specification (ECMAScript) # sec-object.is

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`is`	30	12	22	No	17	9	≤37	30	22	18	9	2.0