How to Defer parsing javascript

gistfile1.html

<script defer="defer" type="text/javascript">
  window.onload=function(){
		var mycode;
		mycode=document.createElement("script");
		mycode.type="text/javascript";
		mycode.src="<?php bloginfo('template_url') ?>/js/your_script.js";
		document.getElementsByTagName("head")[0].appendChild(mycode);
	}
</script>