I made this code, but I am not understanding how JavaScript is handling the swapping??? (I have seen this before in an article but didnt explain)

What is the name or official term of what I want to understand below in JavaScript??


I have never been able to find a clear article explanation of what arrays do behind the scenes when swapping numbers (I think this is a short way of replacing values, if im not wrong).




const swapNumbers = (numbers: number[]) => {
const swap = numbers.map((x: number, index: number) =>
index % 2 !== 0 ? numbers[index - 1] : index === numbers.length - 1 && numbers.length % 2 !== 0 ? numbers[index] : numbers[index + 1]);

console.log(swap);
};

swapNumbers([1, 2, 3, 4]);
swapNumbers([1, 2, 5, 6, 8]);





I want to understand what this is exactly doing (I want to understand the long way)... is this numbers[index + 1] (short way, which is placing the next number in line) the same as this (long way) numbers[index + 1] = numbers[index] or numbers[index + 1] = x?


What is the condition to be able to do this? (is it only in maps and other es6 functions? or can I use this in a regular for loop e.g. numbers[index - 1];?)