为什么我的js没有运行
这个代码有点长,不过都很容易懂,我是初学者,麻烦帮我看看为什么我的js没有运行起来
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
   <head>
     <base href="<%=basePath%>">      
     <title>My JSP 'index.jsp' starting page</title>
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">     
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->
	<script language = "javascript" type = "text/javascript" src = "jquery-1.7.2.js"/></script>
	<script language = "javascript" type = "text/javascript" src = "ajax.js"/></script>
	<script language = "javascript" type = "text/javascript" src = "username.js"/></script>
   </head>    
   <body>
     <center>
     <h3>测试ajax</h3>
     <form action="#" method = "post">
     <table>      
     <tr>
     <td>用户名:</td>
     <td><input type = "text" name = "username" id = "user_name"onchange="javascript:checkname()"></td>
     <td><div id = "point_out"></div></td>
     </tr>      
     <tr>
     <td>密码:</td>
     <td><input type = "password" name = "password" id = "user_password" onchange="javascript:password()"></td>
     <td><div id = "point_out2"></div></td>
     </tr>      
     <tr>
     <td>再次输入密码:</td>
     <td><input type = "password" name = "password2" id = "user_password2" onchange="javascript:checkright()"></td>
     <td><div id = "point_out3"></div></td>
     </tr>      
     </table>
     </form>
     </center>
   </body>
</html>
js文件是这样的
function checkname(){	
	var username = document.getElementById("user_name").value;
	var ajax = creatAjax();
	var url = "/servlet/deal?p"+username;
	ajax.open("GET",url,"true");
	ajax.send();
	ajax.onreadystatechange=function()
	    {
          if (readyState==4 && ajax.status==200)
               {
                     var res = ajax.responseText;
                     var con = "";
                     if(res == 1){
                     	con = "恭喜,该用户名可以注册";
                     }else{
                     	con = "对不起,请换其他用户名";
                     }