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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"


Operator: x-- or --x

, (, x--), .

, (, --x), .

js
let x = 3;
y = x--;

// y = 3
// x = 2

js
let a = 2;
b = --a;

// a = 1
// b = 1

Specification
ECMAScript 2027 LanguageSpecification
# sec-postfix-decrement-operator

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  1. JavaScript
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    118. TypeError: invalid Array.prototype.sort argument (TypeError: Array.prototype.sort argument)
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