setTimeout with Loop in JavaScript

Question

I have a very trivial question. For a simple loop with setTimeout, like this:

for (var count = 0; count < 3; count++) {
    setTimeout(function() {
               


        

Answer 1

think about it like that:

AFTER the 1000*n miliseconds are over, what will be the value of count?

of course it will be 3, because the foor loop ended way earlier than the timeout of 1000*n ms.

in order to print 1,2,3 you'll need the following:

for (var count = 0; count < 3; count++) {
    do_alert(num);
}

function do_alert(num) {
    setTimeout(function() {
        alert("Count = " + num);
    }, 1000 * num);
}

a different approach is to make it a closure function (explained well in JavaScript closures vs. anonymous functions)

for (var count = 0; count < 3; count++) {
    (function(num){setTimeout(function() {
        alert("Count = " + num);
    }, 1000 * num)})(count);
}

these two code samples will actually work similarly.

the first sample calls a named function (do_alert) each iteration.

the second sample calls a CLOSURE anonymous function (which is just like do_alert) each iteration.

it's all a matter of SCOPE.

hope that helps.