请老师检查代码

来源：4-8 编程练习

慕仙0287733

2020-04-29 22:00:05

<!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*/
        //定义各个元素
        var nums = {
            num1: document.getElementById('num1').value,
            num2: document.getElementById('num2').value,
            result: document.getElementById('result'),
            symbol: document.getElementById('operate').value,
        };
        //定义运算函数
        var operate = {
            add: function (a,b) {
                return parseFloat(a) + parseFloat(b);
            },
            subtract: function (a,b) {
                return parseFloat(a) - parseFloat(b);
            },
            multiply: function (a,b) {
                return parseFloat(a) * parseFloat(b);
            },
            divide: function (a,b) {
                return parseFloat(a) / parseFloat(b);
            }
        };
        //选择运算符
        var operate_select = nums.symbol;
        var type;
        switch (operate_select) {
            case '+':
                type = operate.add;
                break;
            case '-':
                type = operate.subtract;
                break;
            case '*':
                type = operate.multiply;
                break;
            case '/':
                type = operate.divide;
                break;
        }
        //计算结果
        nums.result.value= type(nums.num1,nums.num2);
    }
</script>
</body>
</html>