Instead of a "forever" loop, in Javascript we use timers. A timer is just something that causes an event to occur at some point in the future. There are two types:

• Timers that cause a single event in the future
• Timers that cause repeating events

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Timers need two things to make them work:

• You make a function that gets called in the future
  function MyTimerHandler () { // Do something interesting }
• You declare when that function should be called
  setInterval(MyTimerHandler, 500);

The "500" in the call to setInterval is how long between each "tick of the timer", expressed in millseconds -- thousandths of a second. 500 milliseconds is half a second.