Javascript Import Javascript

<script type="text/javascript">
 function importScript(url)
 {
  var tag = document.createElement("script");
  tag.type = 
  tag.src = url;
  document.getElementByTagName("head")[0].appedChild(tag);
 }
 
 window.onload = function()
 {
  importScript("testing.js");
 };
</script>