怎么不弹出东东来呢,超超超简单的小问题

<html>
  <head>
    <base href="<%=basePath%>">
    <title>My JSP 'index.jsp' starting page</title>
<script language="javascript">
function a(){
    b("jump");
}
function b(var arg){
    alert(arg);
}
</script>
  </head>
  <body>
   <input  type="button" value="button" onclick = "a()"/>
  </body>
</html>我了个去,怎么连jump都没有弹出来????什么情况呀....悲剧...方法调用哪里调错了呀????????jsp