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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<div class="box">
<h2>计算器</h2>
<form action="">
<table>
<tr>
<td><input type="text" name="opt1"></td>
<td>
<select name="option" id="">
<option value="null">选择运算符</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"></td>
<td><button type="button">计算</button></td>
</tr>
<tr>
<td style="text-align: right" colspan="2">结果：</td>
<td style="text-align: left"><h3 id="res" style="color: orangered"></h3></td>
</tr>
</table>
</form>
</div>
<script>
//获取操作数、按钮、结果
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 res = document.getElementById('res');
//给按钮添加事件，进行计算
btn.onclick = function () {
let data1 = 0;
let data2 = 0;
if(opt1.value.length === 0){
alert('第一个数不能为空');
opt1.focus();
return false;
}else if(isNaN(opt1.value)){
alert('第一个数不是数字');
opt1.focus();
return false;
}else if(opt2.value.length === 0){
alert('第二个数不能为空');
opt1.focus();
return false;
}else if(isNaN(opt2.value)){
alert('第二个数不是数字');
opt1.focus();
return false;
}else{
data1 = parseFloat(opt1.value);
data2 = parseFloat(opt2.value);
}
let option = opt.value;
let tmp = 0;
let flag = '';
switch (option) {
case 'null':
alert('请选择操作类型');
opt.focus();
return false;
case 'add':
flag = '+';
tmp = data1 + data2;
break;
case 'sub':
flag = '-';
tmp = data1 - data2;
break;
case 'mul':
flag = '*';
tmp = data1 * data2;
break;
case 'div':
flag = '÷';
if(data2 === 0){
alert('除数不能为0');
opt2.focus();
return false;
}else {
tmp = data1 / data2;
tmp = Math.round(tmp * 100)/100
}
break;
}
res.innerHTML = tmp ;
}
</script>
<style>
.box{
text-align: center;
background-color: lightgrey;
border: black 1px solid;
width: 600px;
height: 200px;
overflow:hidden;
margin: 30px auto;
border-radius: 15px;
}
table{
margin: auto;
}
button{
width: 50px;
text-align: center;
background: cornflowerblue;
border: none;
color: white;
}
button:hover{
cursor: pointer;
background:orange;
}
</style>
</body>
</html>点击 "运行实例" 按钮查看在线实例
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