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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 bothfalse
- both strings of the same length with the same characters
- both the same object
- both numbers and
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 ===
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
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
Polyfill for non-ES6 browsers
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 using the following code at the beginning of your scripts. This will allow you to use Object.is()
when there is no built–in support.
if (!Object.is) { Object.is = 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; } }; }
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Object.is' in that specification. |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) The definition of 'Object.is' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 30 | 22 (22) | No support | (Yes) | 9 |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | No support | ? | 22.0 (22) | No support | No support | 9 |
See also
- Equality comparisons and sameness — a comparison of all three built-in sameness facilities