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® 2026 Language Specification # sec-postfix-increment-operator |
