老师，我有一个问题

来源：4-8 编程练习

小林龙

2020-03-08 16:38:28

var operate =(function () {
   function operate(name,num1,num2) {
   if (!operation[name]){
     throw new Error("不存在名为"+name+"的属性");
   }
   return operation[name].apply(operation,[].slice.call(arguments,1,arguments.length));
   }

这是我跟着老师一起写的代码，在这里老师后定义operation这个对象然后调用对象中的加减乘除，没有问题

<!DOCTYPE html>
<html>
<head>
    <title> 事件</title>
</head>
<body>
    <input type='text' id='num1' />

    <select id='operate'>
        <option value='+'>+</option>
        <option value="-">-</option>
        <option value="*">*</option>
        <option value="/">/</option>
    </select>
    <input type='text' id='num2' />

    <input type='button' value=' = ' onclick="count()" />

    <input type='text' id='result' />


    <script type="text/javascript">
        function count() {
            /*此处写代码*/
            var num1 = document.querySelector("#num1"),
                num2 = document.querySelector("#num2"),
                operate = document.querySelector("#operate"),
                result = document.querySelector("#result");

             var countResult = {
                 addHandler:function(num1,num2){
                    return +num1 + +num2;
                },
                 abtractHandler:function(num1,num2){
                    return num1-num2;
                },
                 multiplyHandler:function (num1,num2){
                    return num1*num2;
                },
                 divideHandler:function(num1,num2){
                    return num1/num2;
                }
            };

            switch (operate.value){
                case "+" :
                resultOutput(countResult["addHandler"](num1.value,num2.value));
                break;
                case "-" :
                resultOutput(countResult["abtractHandler"](num1.value,num2.value));
                break;
                case "*" :
                resultOutput(countResult["multiplyHandler"](num1.value,num2.value));
                break;
                case "/" :
                resultOutput(countResult["divideHandler"](num1.value,num2.value));
                break;
            };




            function resultOutput(Output){
                result.value = Output;
            };

        }
    </script>
</body>
</html>