javascript封装addLoadEvent实现页面同时加载执行多个

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