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Teacher's comments：
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今天学习了 javascript中的DOM与事件操作基础
代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>计算器</title>
<style>
.box {
width: 500px;
height: 200px;
background-color: #efefef;
border: 1px solid lightgrey;
text-align: center;
margin: 20px auto;
border-radius: 15px;
box-shadow: 2px 2px 2px #999;
}
table {
margin: auto;
/*border: 1px solid red;*/
}
td {
width: 100px;
height: 30px;
padding: 5px 10px;
}
input, select {
width: 100%;
height: 100%;
border: none;
text-align: left;
padding-left: 15px;
}
button {
width: 100%;
height: 100%;
border: none;
background-color: skyblue;
color: white;
}
button:hover {
cursor: pointer;
background-color: coral;
width: 110%;
height: 110%;
}
</style>
</head>
<body>
<div class="box">
<h2>计算器</h2>
<form>
<table>
<tr>
<td><input type="text" name="opt1" placeholder="操作数1"></td>
<td>
<select name="option" id="">
<option value="null">请选择操作</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>
<td><button type="button">计算</button></td>
</tr>
<tr>
<td align="right" colspan="2"><h3>结果:</h3></td>
<td align="left" colspan="2"><h3 id="result"></h3></td>
</tr>
</table>
</form>
</div>
<script>
//1. 获取操作数,按钮,结果占位符
let opt1 = document.getElementsByName('opt1')[0];
let opt2 = document.getElementsByName('opt2')[0];
let opt = document.getElementsByName('option')[0];
let btn = document.getElementsByTagName('button')[0];
let result = document.getElementById('result');
//2. 给按钮添加事件,进行计算
btn.onclick = function () {
//操作数初始化
let data1 = 0;
let data2 = 0;
if (opt1.value.length === 0) {
alert('第一个操作数不能为空');
opt1.focus();
return false;
} else if (isNaN(opt1.value)) {
alert('第一个操作数必须为数字');
opt1.focus();
return false;
} else if (opt2.value.length === 0) {
alert('第二个操作数不能为空');
opt2.focus();
return false;
} else if (isNaN(opt2.value)) {
alert('第二个操作数必须为数字');
opt2.focus();
return false;
} else {
data1 = parseFloat(opt1.value);
data2 = parseFloat(opt2.value);
}
//对操作符进行处理
let option = opt.value; // 拿到了用户选择的操作
let temp = 0;
let flag = '';
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 = '/';
//进行除数不能为零的判断和处理
if (data2 === 0) {
alert('除数不能为零');
opt2.focus();
opt2.value = '';
return false;
} else {
temp = data1 / data2;
// 四舍五入,仅保留二位小数
temp = Math.round(temp * 100) / 100;
}
break;
}
let str = '<span style="color:coral">';
str += data1 + ' ' +flag + ' ' + data2 + ' = ' +temp;
str += '</span>';
result.innerHTML = str;
}
</script>
</body>
</html>点击 "运行实例" 按钮查看在线实例
