The strict equality operator (===
) checks whether its two operands are equal, returning a Boolean result. Unlike the equality operator, the strict equality operator always considers operands of different types to be different.
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Syntax
x === y
Description
The strict equality operators (===
and !==
) use the Strict Equality Comparison Algorithm to compare two operands.
- If the operands are of different types, return
false
. - If both operands are objects, return
true
only if they refer to the same object. - If both operands are
null
or both operands areundefined
, returntrue
. - If either operand is
NaN
, returnfalse
. - Otherwise, compare the two operand's values:
- Numbers must have the same numeric values.
+0
and-0
are considered to be the same value. - Strings must have the same characters in the same order.
- Booleans must be both
true
or bothfalse
.
- Numbers must have the same numeric values.
The most notable difference between this operator and the equality (==
) operator is that if the operands are of different types, the ==
operator attempts to convert them to the same type before comparing.
Examples
Comparing operands of the same type
console.log("hello" === "hello"); // true console.log("hello" === "hola"); // false console.log(3 === 3); // true console.log(3 === 4); // false console.log(true === true); // true console.log(true === false); // false console.log(null === null); // true
Comparing operands of different types
console.log("3" === 3); // false console.log(true === 1); // false console.log(null === undefined); // false
Comparing objects
const object1 = { name: "hello" } const object2 = { name: "hello" } console.log(object1 === object2); // false console.log(object1 === object1); // true
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Equality operators' in that specification. |
Browser compatibility
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Strict equality (a === b ) | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support 4 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support 0.1.100 |
Legend
- Full support
- Full support