Fix timer starting on page load

A simple Javascript timer tha开发者_开发技巧t runs for 30 seconds and displays a message once it reaches 0. I cant figure out how to get it to start when a button is pressed instead of on pageload. Any help is appreciated :)

<script type="text/javascript">
var sec = 30;   // set the seconds
var min = 00;   // set the minutes

function countDown() {
  sec--;
  if (sec == -01) {
    sec = 59;
    min = min - 1;
  } else {
   min = min;
  }
if (sec<=9) { sec = "0" + sec; }
  time = (min<=9 ? "0" + min : min) + " min and " + sec + " sec ";
if (document.getElementById) { theTime.innerHTML = time; }
  SD=window.setTimeout("countDown();", 1000);
if (min == '00' && sec == '00') { sec = "00"; window.clearTimeout(SD); alert("Too slow."); }
}

function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      if (oldonload) {
        oldonload();
      }
      func();
    }
  }
}

addLoadEvent(function() {
  countDown();
});
</script>

<button onclick='countDown();'>Click Me</button>

And just don't call addLoadEvent() at all.

Add event listener to the button in the load function and then call countDown

 addLoadEvent(function() {
   var el = document.getElementById("startButton");   
     el.addEventListener("click", countDown, false); 
});

Here the full example link

Here's a full sample with start/stop and remaining time display.

var gTimer = null

function endOfTimer() {
    console.log("here");
    window.alert('Too slow');
}

function start() {
    gTimer = window.setTimeout('endOfTimer', 1 * 1000);
}