第11章 3_29javascript入门与实战-作业 - PHP学习笔记

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<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">

    <title>Document</title>
    <style type="text/css">
        .box {
            width: 500px;
            height: 200px;
            background-color: #efefef;
            border: 1px solid lightgray;
            text-align: center;
            margin: auto;
            margin: 20px auto;
            color: #636363;
            border-radius: 15px;
            box-shadow: 2px 2px 2px #999;
        }
style

    </style>
</head>
<body>

<!-- 1.获取页面元素的方法; 2.条件判断语句的使用方法 3.事件方法函数的作用 -->
<div class="box">
    <h2>迷你计算器</h2>
    <bs-3></bs-3>
    <from>
        <table>
            <tr>
                <td><input type="text" name="opt1" placeholder="操作数1"></td>        <!-- 输入操作数1-->
                <td>
                    <select name="option">                                           <!--选择运算符选-->
                        <option value="null"></option>
                        <option value="add">+</option>
                        <option value="sub">-</option>
                        <option value="mul">*</option>
                        <option value="div">/</option>
                    </select>
                </td>
                <td><input type="text" name="opt2" placeholder="操作数2"></td>        <!--输入操作数2-->
                <td><button type="button">计算</button></td>                          <!--计算按钮-->
            </tr>
            <tr>
                <td colspan="2" align="right"><h3>结果</h3></td>                      <!--显示结果-->
                <td colspan="2" align="left"><h3 id="placeholder"></h3></td>
            </tr>
        </table>
    </from>
</div>
<script type="text/javascript">
    //1. 获取操作数，按钮与结果占位符
    var opt1 = document.getElementsByName('opt1')[0]   //获取第一个数
    var opt2 = document.getElementsByName('opt2')[0]   //获取第二个数
    var opt  = document.getElementsByName('option')[0] //获取运算符

    var btn =  document.getElementsByTagName('button')[0]//获取按钮
    var placeholder = document.getElementById('placeholder') //获取运算结果


    //2.给按钮添加事件,执行计算操作
    btn.onclick = function(){
        // var data1 = parseFloat(opt1.value)
        // var data2 = parseFloat(opt2.value)


        if (opt1.value.length == 0 ) {          //判断第一个数不能为空
            alert('第一个操作数不能为空')
            opt1.focus()
            return false
        } else if (isNaN(opt1.value)) {         //判断第一个数是否为数字
            aleat('第一个数必须为数字')
            opt1.focus()
            return false
        } else if  (opt2.value.length == 0 ){   //判断第二个数不能为空
            alert('第一个操作不能为空')
            opt2.focus()
            return false
        } else if (isNaN(opt2.value)) {         //判断第二个数是否为数字
            alert('第一个数必须为数字')
            opt2.focus()
            return false
        } else {
            var data1 = parseFloat(opt1.value)    //如果以上条件成立，赋值opt1到 data1
            var data2 = parseFloat(opt2.value)    // 赋值opt2到 data2
        }


        var option  = opt.value
        var temp = 0
        var flag = ''
        var result = ''
        switch (option){
            case 'null':
                alert("请选择操作类型")
                opt.focus()
                return false
            case 'add':
                flag = '+'
                temp = data1 + data2
                break
            case 'sub':
                flag = '-'
                temp = data1 - data2
                break
            case 'mul':
                flag = '*'
                temp = data1 * data2
                break
            case 'div':
                flag = '/'
                if (data2 ==0 ){
                    aleat('除数不能为0，请重新输入')
                    opt2.focus()
                    return false
                } else {
                    temp = data1 / data2
                }
                break
        }

        // placeholder.innerHTML = '<span style="color:coral">'+data1+' '+ flag+' '+ data2+' = '+temp +'</span>'

        var str = '<span style="color:coral">'
        str += data1+' '+flag+' '+data2 + ' = ' + temp
        str += '</span>'
        placeholder.innerHTML = str
    }


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

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