Javascript Question posted in
A very good W3school tutorial can be found here.

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];?)

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2

Answers


  1. 0

    Here it is written in long form.

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

  console.log(swap);
};

const swapNumbers2 = (numbers) => {
    let swap= [];
    for (let index = 0; index < numbers.length; index++) {
        if (index % 2 !== 0) {
            swap.push(numbers[index - 1]);
        }
        else if (index === numbers.length - 1 && numbers.length % 2 !== 0) {
            swap.push(numbers[index]);
        }
        else {
            swap.push(numbers[index + 1]);
        }
    }
    console.log(swap);
}

swapNumbers([1,2,3,4]);
swapNumbers2([1,2,3,4]);
swapNumbers([1, 2, 5, 6, 8]);
swapNumbers2([1, 2, 5, 6, 8]);
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  2. 0

    Here is a simpler alternative in Vanilla JavaScript (swapping in-place):

    const swap=nums=>
  (nums.forEach((x,i,a)=>{
    if(i%2) [a[i-1],a[i]]=[x,a[i-1]]
  }),nums);

[[1,2,3,4],[1,2,5,6,8]].map(a=>
  console.log(swap(a)));
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