js简易计算器

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>简单计算器</title>
</head>
<body>
    <input type="text" id="shu1" size="7">
    <select id="ys">
        <option>+</option>
        <option>-</option>
        <option>*</option>
        <option>/</option>
        <option>%</option>
    </select>
    <input type="text" id="shu2" size="7">
    <button type="button" id="js" value="btn">=</button>
    <p id="jg">结果：</p>
    <script>
     document.getElementById("js").onclick =function(){
         var shu1 = document.getElementById("shu1").value;
         var shu2 = document.getElementById("shu2").value;
         var ys = document.getElementById("ys").value;
         var zhjg =true;
         if(shu1==''||shu2==''){
             alert('输入框不能为空');
             return;
         }
         if(zhjg){
             switch(ys){
                 case '+' :
                 result = "结果：" + ((parseFloat(shu1)*100 + parseFloat(shu2)*100)/100);
                 break;
                 case '-' :
                 result = "结果：" + (shu1 - shu2);
                 break;
                 case '*' :
                 result = "结果：" + (shu1 * shu2);
                 break;
                 case '/' :
                     if(shu2==0){
                         result ="除数不能为0"
                     }else{
                        result = "结果："  + (shu1 / shu2);
                     }
                     break;
                 case '%' :
                    if(shu2==0){
                         result ="除数不能为0"
                    }else{
                         result = "结果："  + (shu1 % shu2);
                     }
                    break;
             }
         }
         document.getElementById('jg').innerHTML=result;
     }
    </script>
</body>
</html>
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