function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      oldonload();
      func();
    }
  }
}
var setHeight = {
	init : function(){
		var container = document.getElementById("main");
		if (container.offsetHeight < 500) {
			container.style.height = "500px";
		}
	}
}
addLoadEvent(setHeight.init);