I don't understand they outputs of this increment example

Question

i found this example online of the pre and post fix examples of incrementing and decrementing a variable. however, i don't understand why it is return x as 4 and subsequently a as 4 in the example. I understand the y values.

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"

Answer 1

等待大神答复