Поясните пожалуйста почему так работает цикл? На выходе получаем 1334 / Explain the output of this code? Why output 1334?

Question

var arr=[1, 2, 3, 4];
var ct=arr.length;
for (var i=0; i<ct; i++) {
ct--;
arr[i]+=i;
}
document.write(arr);

Answer 1

I understand, 1 and 2 it's result of loop and 3, 4 elements of array that don't delete. Thank you👌

Answer 2

1+0 = 1
2+1 = 3
Then it exits from the loop since ct is 2 and i is 2 too meaning that i < ct is false.

Answer 3

Let's go through the code, as if we were a run-time debugger:

arr=[1, 2, 3, 4]
ct = 4

for (var i=0; i<4; i++) {
ct--
// i = 0
// ct = 3
arr[0] = arr[0] + 0 = 1 + 0 = 1

for (var i=1; i<3; i++) {
ct--
// i = 1
// ct = 2
arr[1] = arr[1] + 1 = 2 + 1 = 3

for (var i=2; i<2; i++) {

break;

document.write(arr);

Note that only the first two elements of the array are overwritten, as 1 and 3 respectively.

In the future, you can put more document.write() functions to see what's happening. You can also do what I did, which is to step through it, like a debugger would.

Answer 4

Yes, that's exactly it.