'let' in for loop with setTimeout()

Question

let timer = () => {
  for(let i = 0; i < 5; i ++) {
    setTimeout(() => {
      console.log(i)
    }, i * 1000)
  }
}
timer();

code above will print 0, 1, 2, 3, 4 in 1000ms interval
and if I change let i = 0 into var i = 0, timer() will pring '5' five times in 1000ms interval. So far so good, and I know the differences between let and var
But now I want to print 0, 1, 2, 3, 4 in 1000ms interval, and not using let keyword, so what should I do?
I think I might need to use closure, but I don't know how.
edit: by not using let I mean use var instead

If not `let` or `var`... are you trying to use `const`? I guess I'm not sure what the goal is in not using `let`. — stealththeninja, Jun 06 '19 at 03:28
[Another way](https://repl.it/repls/LongtermRigidLock) using recursion and no simultaneous timeouts. — Paul Rooney, Jun 06 '19 at 03:55

Angel Politis · Accepted Answer · 2019-06-06T03:42:35.993

If you can't use let, you can always use an Immediately Invoked Function Expression:

let timer = () => {
  for (var i = 0; i < 5; i++) {
    (i => {
      setTimeout(() => {
        console.log(i)
      }, i * 1000)
    })(i)
  }
}
timer();

If you're trying to make your code ES5-compatible, you've got to turn the arrow functions into normal functions as well:

var timer = function () {
  for (var i = 0; i < 5; i++) {
    (function (i) {
      setTimeout(function () {
        console.log(i);
      }, i * 1000);
    })(i);
  }
}
timer();

'let' in for loop with setTimeout()

1 Answers1