加减 script函数初识

 <!DOCTYPE html>
 <html lang="en">
 <head>
     <meta charset="UTF-8">
     <title>Title</title>
     <style>
         body{
             margin: 0;
         }
         .c1{
             top: 10px;
             left: 10px;
             position: relative;
             width: 150px;
             height: 22px;
             border: 1px solid black;
             padding-right: -22px;
         }
         .c2{
             position: absolute;
             width: 22px;
             height: 22px;

             line-height: 22px;
             text-align: center;
             background-color: #dce7f4;
             border-right: 1px solid black;
             cursor: pointer;
         }
         .c3{

         }
         .c3 input{
             border: 0;
             padding: 0;
             position: absolute;
             left: 23px;
             width: 104px;
             height: 22px;
             line-height: 22px;
             text-align: center;

         }

         .c4{
             right: 0;
             position: absolute;
             width: 22px;
             height: 22px;
             line-height: 22px;
             text-align: center;
             border-left: 1px solid black;
             background-color: #dce7f4;
             cursor: pointer;
         }

     </style>
 </head>
 <body>
     <div class="c1">
         <div class="c2" onclick="Minus()">-</div>

          <div class="c3">
             <input type="text" id="count" value="0" />
         </div>

         <div class="c4"  onclick="Plus()">+</div>
     </div>
     <script type="text/javascript">
         //定义函数
         function Plus() {
             var old_str = document.getElementById('count').value;
             try{
                 var old_int = parseInt(old_str);
             }catch(e){
                 var old_int = 1
             }
             var new_int = old_int + 1;
             document.getElementById('count').value = new_int;
         }
         function Minus() {
             var old_str = document.getElementById('count').value;
             try{
                 var old_int = parseInt(old_str);
             }catch(e){
                 var old_int = 1
             }
             var new_int = old_int - 1;
             document.getElementById('count').value = new_int;
         }
     </script>
 </body>
 </html>