购物车相关 js

<div class="caigou">
                    <form action="" method="post">
                    <div class="num_box">
                        <a id="sub">-</a>
                        <input id="num" class="num" name="num" value="1">
                        <a id="add">+</a>
                    </div>
                    </form>
                    <div id="zong">
                      <b id="zongjia">{$xianjia}</b>元
                    </div>
                </div>

<script>
   var b_num=document.getElementById('num');
   var b_sub=document.getElementById('sub');
   var b_add=document.getElementById('add');
  
   var b_zongjia=document.getElementById('zongjia');
   var b_danjia=parseInt(b_zongjia.innerHTML);
   //只能是数字
   b_num.onkeyup=function(){this.value=this.value.replace(/[^0-9]/g,'');
   
   jiesuan()}
   b_num.onafterpaste=function(){this.value=parseInt(this.value.replace(/[^0-9]/g,''));jiesuan()}
   //禁止选中
   b_sub.onselectstart=function(){ return false;}
   b_add.onselectstart=function(){ return false;}
   //加减计算
   b_sub.onclick=function(){
       if(b_num.value<=1){ return false}
        b_num.value = parseInt(b_num.value)-1;
        jiesuan()
       }
   b_add.onclick=function(){
       b_num.value = parseInt(b_num.value)+1;
       jiesuan()
       }
   
   
   
   function jiesuan(){
      if(b_num.value==""){
          b_num.value=0;
          b_zongjia.innerHTML=0; return} 
      b_zongjia.innerHTML= parseInt(b_num.value)*b_danjia;
       }
    //禁止回车
   b_num.onfocus=function(){
   
   window.onkeydown=function(event){
       if(event.keyCode==13||event.keyCode==109||event.keyCode==107){return false;}

       }
  }
       
      b_num.onblue=function(){
   window.onkeydown=function(){};
       }
       
   
   </script>