Increment (++)
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
The increment (++
) operator increments (adds one to) its operand and returns the value before or after the increment, depending on where the operator is placed.
Try it
let x = 3;
const y = x++;
console.log(`x:${x}, y:${y}`);
// Expected output: "x:4, y:3"
let a = 3;
const b = ++a;
console.log(`a:${a}, b:${b}`);
// Expected output: "a:4, b:4"
Syntax
x++
++x
Description
The ++
operator is overloaded for two types of operands: number and BigInt. It first coerces the operand to a numeric value and tests the type of it. It performs BigInt increment if the operand becomes a BigInt; otherwise, it performs number increment.
If used postfix, with operator after operand (for example, x++
), the increment operator increments and returns the value before incrementing.
If used prefix, with operator before operand (for example, ++x
), the increment operator increments and returns the value after incrementing.
The increment operator can only be applied on operands that are references (variables and object properties; i.e. valid assignment targets). ++x
itself evaluates to a value, not a reference, so you cannot chain multiple increment operators together.
++(++x); // SyntaxError: Invalid left-hand side expression in prefix operation
Examples
Postfix increment
let x = 3;
const y = x++;
// x is 4; y is 3
let x2 = 3n;
const y2 = x2++;
// x2 is 4n; y2 is 3n
Prefix increment
let x = 3;
const y = ++x;
// x is 4; y is 4
let x2 = 3n;
const y2 = ++x2;
// x2 is 4n; y2 is 4n
Specifications
Specification |
---|
ECMAScript® 2025 Language Specification # sec-postfix-increment-operator |
Browser compatibility
Report problems with this compatibility data on GitHubdesktop | mobile | server | ||||||||||||
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Increment ( ++ ) |
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