Strict equality (===)

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

js

x === y

Description

The strict equality operators (=== and !==) provide the IsStrictlyEqual semantic.

  • 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 are undefined, return true.
  • If either operand is NaN, return false.
  • 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 both false.

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

js

"hello" === "hello"; // true
"hello" === "hola"; // false

3 === 3; // true
3 === 4; // false

true === true; // true
true === false; // false

null === null; // true

Comparing operands of different types

js

"3" === 3; // false
true === 1; // false
null === undefined; // false
3 === new Number(3); // false

Comparing objects

js

const object1 = {
  key: "value",
};

const object2 = {
  key: "value",
};

console.log(object1 === object2); // false
console.log(object1 === object1); // true

Specifications

Specification
ECMAScript Language Specification
# sec-equality-operators

Browser compatibility

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See also