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Correction status：qualified
Teacher's comments：
Collection
Collection
这一节课讲的是JavaScript中DOM与事件的操作，并用实际案例来演示
代码
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport"
content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
.box{
width: 500px;
height: 200px;
background-color: #efefef;
border: 1px solid lightgrey;
text-align: center;
margin: 20px auto;
color: #636363;
border-radius: 15px;
box-shadow: 2px 2px 2px #999;
}
table {
margin: auto;
}
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>
var opt1=document.getElementsByName('opt1')[0];
var opt2=document.getElementsByName('opt2')[0];
var opt=document.getElementsByName('option')[0];
var btn=document.getElementsByTagName('button')[0];
var result=document.getElementById('result');
btn.onclick=function () {
var data1=0;
var 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);
}
var option=opt.value;
var temp=0;
var 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='/';
if (data2===0){
alert('除数不能为零');
opt2.focus();
opt2.value='';
return false;
}else {
temp = data1/data2;
temp=Math.round(temp*100)/100;
}
break;
}
var str=data1+ ' '+flag+' '+data2+'='+temp;
result.innerHTML = str;
}
</script>
</body>
</html>点击 "运行实例" 按钮查看在线实例
预览图
![)2$BU]BJRG(YVZQ}}P@7EGI.png](https://img.php.cn//upload/image/929/252/479/1536818599630546.png "1536818599630546.png")
总结
1、DOM: Document Object Model; 文档对象模型
2、禁止a的点击链接功能用 return false；
3、getElementsByTagName用标签名获取，getElementById用id获取
4、onlick（）点击事件