怎样操作JS文件内加载jquery.js（附代码）

// by firefoxmmx 
var script=document.createElement("script"); 
script.type="text/javascript"; 
script.src="jquery.js"; 
document.getElementsByTagName('head')[0].appendChild(script); 
setTimeout(function(){ 
$(document).ready(function(){ 
 $("#bt").click(function(){ 
  alert('Hello World'); 
 }); 
}); 
},100);

 
 
 <script></script> 
 
 
<input> 
 

<script>
 document.write("<script src=&#39;test.js&#39;><\/script>");
</script>

<script></script><script>
 s1.src="test.js"
</script>

<script>
 var oHead = document.getElementsByTagName(&#39;HEAD&#39;).item(0);
 var oScript= document.createElement("script");
 oScript.type = "text/javascript";
 oScript.src="test.js";
 oHead.appendChild( oScript);
</script>