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.
-- 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 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. 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
let x = 3; const y = x--; // x is 2; y is 3 let x2 = 3n; const y2 = x2--; // x2 is 2n; y2 is 3n
let x = 3; const y = --x; // x is 2; y = 2 let x2 = 3n; const y2 = --x2; // x2 is 2n; y2 is 2n
|ECMAScript Language Specification |
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