My JavaScript loop is an infinite loop?

Javascript has function-level block execution. One function runs to completion before another function is given ability to execute. Your while loop is maintaining the execution baton, so the other functions in setTimeout are never given a chance.

although javascript is called asynchonous in this case it does not call the subtract function until the first one is finished. (details http://ejohn.org/blog/how-javascript-timers-work/)

this should work

var number = 30;

setTimeout(function() {
    console.log(number);
    number = number - 1;
}, 1000);

setInterval is the function to set a function to run periodically. https://developer.mozilla.org/en-US/docs/Web/API/Window.setInterval

var number = 30;
var countdown = true;
var timer;

function update(){
   console.log(number);
   number = number - 1;
   if (number === 0)
      clearInterval(timer);
}


timer = setInterval(update, 1000);

When using the setTimeout function you actualy call a function after X miliseconds (in this case X=1000, which is 1 second).

'While' is the function you want to do the countdown with, right? So in your subtract function just write:

console.log(number);
number = number - 1;

You can also drop the subtract function and just write:

while(countdown === true) {
    console.log(number);
    number = number - 1;
    if(number === 0) {
        countdown = false;
    }
}

Or drop the while function:

function subtract() {
    id(countdown === true)
    setTimeout(function() {
        console.log(number);
        number = number - 1;
        subtract();
    }, 1000);
    else countdown = false;
}
subtract();