javascript method is called 2 times

Question

I am adding jQuery and swf library dynamically, onloading these libraries i am calling a method but the method is called twice, it works fine on local but on website it(methodCall()) fires 2 times.

function importJS(src, look_for, onload) {
    //if already exists
    if (eval("typeof " + look_for) != 'undefined'){
        wait_for_script_load(look_for, onload);
        return 0;
    }

   var s = document.createElement('script');
   s.setAttribute('type', 'text/javascript');
   s.setAttribute('src', src);
   if (onload) wait_for_script_load(look_for, onload);
   var head = document.getElementsByTagName('head')[0];
   if (head) {
     head.appendChild(s);
   } else {
     document.body.appendChild(s);
   }
 }

function wait_for_script_load(look_for, callback) {
   var interval = setInterval(function() {
     if (eval("typeof " + look_for) != 'undefined') {
       clearInterval(interval);
       callback();
     }
   }, 50);
 }
(function(){   
   importJS('http://xyz.com/jquery.js', 'jQuery', function() {     
     importJS('http://xyz.com/swfobject.js', 'swfobject', function() {
         methodCall();
       });
   });
 })();