Decrement (--)
The decrement (--) operator decrements (subtracts one from) its operand and returns the value before or after the decrement, depending on where the operator is placed.
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Syntax
x--
--x
Description
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. valid assignment 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 = 2
// y = 3
Prefix decrement
let x = 3;
const y = --x;
// x = 2
// y = 2
Specifications
| Specification |
|---|
| ECMAScript Language Specification # sec-postfix-decrement-operator |
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