JS运行结果显示不出来


<body>
        <h3>简易计算器h3>
        <form>
            <input type="text" size ="5",id="num1" value=""/>
            <select id="operator">
             <option value="+" selected="selected">+option>
             <option value="-" >-option>
             <option value="*" >*option>
             <option value="/">/option>
            select>
           
            <input type="text" size="5" id="num2" value=""/>
            <input type="button" value="=" id="ok"/>
            <input type="text" size="16" id="result" readonly="true">
        form>    
body>


<script>
    var oNum1=document.getElementById("num1");
    var oNum2=document.getElementById("num2");
    var oOper=document.getElementById("operator");
    var oOk=document.getElementById("ok");
    var res ="";
    oOk.onclick=function(){
     var num1=parseFloat(oNum1.value);
     var num2=parseFloat(oNum2.value);
     var oper=oOper.value;
     if (num1 && num2){
         switch(oper){
case "+":res =num1+num2; break;
case "-":res =num1-num2; break;
case "*":res =num1*num2; break;
case "/" :res =num1/num2; break;
 

         }

     }else{
         res ="请输入不为0的数值";
     }


document.getElementById('result').value=res;
}

script>

错误显示

img

img

id="num1"前的逗号删了