Thedecrement (--) operator decrements (subtracts one from) its operand and returns the value before or after the decrement, depending on where the operator is placed.

Try it

let x = 3;const y = x--;console.log(`x:${x}, y:${y}`);// Expected output: "x:2, y:3"let a = 3;const b = --a;console.log(`a:${a}, b:${b}`);// Expected output: "a:2, b:2"

Syntax

x----x

Description

The-- operator is overloaded for two types of operands: number andBigInt. It firstcoerces the operand to a numeric value and tests the type of it. It performs BigInt decrement if the operand becomes a BigInt; otherwise, it performs number decrement.

If used postfix, with operator after operand (for example,x--), the decrement operator decrements and returns the value before decrementing.

If used prefix, with operator before operand (for example,--x), the decrement operator decrements and returns the value after decrementing.

The decrement operator can only be applied on operands that are references (variables and object properties; i.e., validassignment targets).--x itself evaluates to a value, not a reference, so you cannot chain multiple decrement operators together.

--(--x); // SyntaxError: Invalid left-hand side expression in prefix operation

Examples

Postfix decrement

let x = 3;const y = x--;// x is 2; y is 3let x2 = 3n;const y2 = x2--;// x2 is 2n; y2 is 3n

Prefix decrement

let x = 3;const y = --x;// x is 2; y = 2let x2 = 3n;const y2 = --x2;// x2 is 2n; y2 is 2n

Specifications

Browser compatibility

See also

• Addition (+)
• Subtraction (-)
• Division (/)
• Multiplication (*)
• Remainder (%)
• Exponentiation (**)
• Increment (++)
• Unary negation (-)
• Unary plus (+)