js点击密码输入框密码显示隐藏

很多密码框都有个眼睛标记，点击能显示密码。原理就是点击切换password为text等显示

下面上代码

 1 <!DOCTYPE html>
 2 <html>
 3     <head>
 4         <meta charset="utf-8">
 5         <title></title>
 6         <style type="text/css">
 7             .pass{
 8                 width:200px;
 9                 height: 20px;
10             }
11         </style>
12         <script>
13             window.onload=function(){
14                 var btn=document.getElementById("btn");
15                 var pass=document.getElementById("pass")
16                 btn.onmousedown=function(){
17                     pass.type="number"
18                 };
19                 btn.onmouseup=btn.onmouseout=function(){
20                     pass.type="password"
21                 }
22             }
23         </script>
24     </head>
25     <body>
26         <input type="password" name="" id="pass" value="123456" class="pass"/>
27         <input type="button" name="" id="btn" value="点击显示" />
28     </body>
29 </html>