4-8 编程练习作业提交

来源：4-8 编程练习

MiMicccc

2021-05-19 15:45:20

<!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*/
            //获取元素
            var wrapElem = {
                num1: document.getElementById('num1'),
                num2: document.getElementById('num2'),
                result: document.getElementById('result'),
                operate: document.getElementById('operate')
            };

            // 运算方法
            var operations = {
                add: function(num1, num2) {
                    return +num1 + +num2;
                },
                subtract: function(num1, num2) {
                    return num1 - num2;
                },
                multiply: function(num1, num2) {
                    return num1 * num2
                },
                divide: function(num1, num2) {
                    return num1 / num2;
                }
            };

            // switch 方法判断并计算+-*/
            var operate = function(num1, num2) {
                switch (wrapElem.operate.value) {
                    case '+':
                        return operations.add(num1, num2);
                        break;
                    case '-':
                        return operations.subtract(num1, num2);
                        break;
                    case '*':
                        return operations.multiply(num1, num2);
                        break;
                    case '/':
                        return operations.divide(num1, num2);
                        break;
                }
            };

            // 更新输出结果
            function outputResult(res) {
                result.value = res;
            }
            outputResult(operate(wrapElem.num1.value, wrapElem.num2.value));
        };
    </script>
</body>

</html>