How does this array and loop work?

Question

JavaScript

Can you please explain how this array works?

var array = [1,2,3,4,5,6,7,8];
    for (var i = 0; i < (array.length / 2); i++) {
        array[i] = [array[i],array[array.length - i - 1]];
        array[array.length - i - 1] = array[i][0];
        array[i] = array[i][1];
    }
    document.write(array);

I can not understand what value i will be in the 3rd line at the end

Answer 1

// i === 0
array[i] = [array[i],array[array.length - i - 1]]; // [[1, 8], 2, 3, 4, 5, 6, 7, 8]
array[array.length - i - 1] = array[i][0]; // [[1, 8], 2, 3, 4, 5, 6, 7, 1]
array[i] = array[i][1]; // [8, 2, 3, 4, 5, 6, 7, 1]
// и т.д.

Answer 2

And if you press F12 and run the code in the console?
First, an array of two elements is temporarily written to the array cell, its own and the mirror on the reverse side. Then the values ​​are returned but swapped. In order not to swap elements twice, the loop goes only to the middle of the length.

Answer 3

Substitute the values ​​and it will become clearer

var array = [1,2,3,4,5,6,7,8];
    for (var i = 0; i < 4 /*(8 / 2)*/; i++) {
        array[0] = [array[0],array[array.length - 0 - 1]];
        array[array.length - 0 - 1] = array[0][0];
        array[0] = array[0][1];
     }
// Следующая итерация i = 1, i < 4 -> да 
        array[1] = [array[1],array[array.length - 2]];
        array[array.length - 2] = array[1]0];
        array[1] = array[1][1];
// Следующая итерация i = 2, i < 4 -> да 
         array[2] = [array[2],array[array.length - 3]];
        array[array.length - 3] = array[2]0];
        array[2] = array[2][1];
// Следующая итерация i = 3, i < 4 -> да 
         array[3] = [array[3],array[array.length - 4]];
        array[array.length - 4] = array[3]0];
        array[3] = array[3][1];
// Следующая итерация i = 4, i < 4 -> нет, выходим из цикла 
 document.write(array);