This is a new technology, part of the ECMAScript 2015 (ES6) standard .
This technology's specification has been finalized, but check the compatibility table for usage and implementation status in various browsers.

The method determines whether two values are the same value.

Syntax, value2);


The first value to compare.
The second value to compare.

Return value

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

Description 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 (if they are not the same Type) before testing for equality (resulting in such behavior as "" == false being true), but 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 treats Number.NaN as not equal to NaN.

Examples'foo', 'foo');     // true, window);   // true'foo', 'bar');     // false[], []);           // false

var test = { a: 1 };, test);       // true, null);       // true

// Special Cases, -0);            // false, -0);           // true, 0/0);         // true

Polyfill for non-ES6 browsers 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 using the following code at the beginning of your scripts. This will allow you to use when there is no built–in support.

if (! { = function(x, y) {
    // SameValue algorithm
    if (x === y) { // Steps 1-5, 7-10
      // Steps 6.b-6.e: +0 != -0
      return x !== 0 || 1 / x === 1 / y;
    } else {
      // Step 6.a: NaN == NaN
      return x !== x && y !== y;


Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of '' in that specification.
Standard Initial definition.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 30 22 (22) Not supported (Yes) Not supported
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support Not supported ? 22.0 (22) Not supported Not supported Not supported

See also

Document Tags and Contributors

Last updated by: fscholz,