How do I emulate the push method?

Using the array example:

massive6 = [100, 200, 300, 400, 700, 121];

I seem to understand the logic, but I can't get to the truth:

btn6.onclick = f6;

function f6() {
    for (let i = 0; i < massive6.length; i++) {
        massive6[massive6.length - 1] = input6.value;
    }
    out6.textContent = massive6;
}

массивы javascript push

Author: aynurbeing, 2021-02-03

Source