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.
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 Language Specification # sec-equality-operators |
Browser compatibility
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