<select></select>
select里面通常跟option配合使用
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="x-ua-compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Title</title>
</head>
<body>
<div>
<form action="http://www.baidu.com" method="get">
<div>
<!-- 下拉框 -->
<select>
<option>广州</option>
<option>深圳</option>
<option>山东</option>
<option>北京</option>
</select>
</div>
</form>
</div>
</body>
</html>
加上name属性 提交后台，让他提交到后台 在每个<option>里面加value
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="x-ua-compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Title</title>
</head>
<body>
<div>
<form action="http://www.baidu.com" method="get">
<div>
<!-- 下拉框 -->
<select name="sel">
<option value="1">广州</option>
<option value="2">深圳</option>
<option value="3">山东</option>
<option value="4">北京</option>
</select>
</div>
<input type="submit" value="提交">
</form>
</div>
</body>
</html>
url上显示提交的值
select的size属性
size取值大于1的话，则为滚动列表，否则就是下拉选项框，默认size等于1
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="x-ua-compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Title</title>
</head>
<body>
<div>
<form action="http://www.baidu.com" method="get">
<div>
<!-- 下拉框 -->
<select name="sel" size="3">
<option value="1">广州</option>
<option value="2">深圳</option>
<option value="3">山东</option>
<option value="4">北京</option>
</select>
</div>
<input type="submit" value="提交">
</form>
</div>
</body>
</html>
select的multiple属性
multiple属性设置多选，该属性出现在<select>中,那么就允许多选(针对滚动列表)
按着ctrl选多个
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="x-ua-compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Title</title>
</head>
<body>
<div>
<form action="http://www.baidu.com" method="get">
<div>
<!-- 下拉框 -->
<select name="sel" size="3" multiple>
<option value="1">广州</option>
<option value="2">深圳</option>
<option value="3">山东</option>
<option value="4">北京</option>
</select>
</div>
<input type="submit" value="提交">
</form>
</div>
</body>
</html>
提交后台拿到两个选中值
select标签的selected 设置默认值
selected预选中，注意：如果不设置selected属性的话，那么选项框中的第一项会默认被选中。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="x-ua-compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Title</title>
</head>
<body>
<div>
<form action="http://www.baidu.com" method="get">
<div>
<!-- 下拉框 -->
<select name="sel">
<option value="1">广州</option>
<option value="2">深圳</option>
<option selected value="3">山东</option>
<option value="4">北京</option>
</select>
</div>
<input type="submit" value="提交">
</form>
</div>
</body>
</html>
单选框
多选项
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="x-ua-compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Title</title>
</head>
<body>
<div>
<form action="http://www.baidu.com" method="get">
<div>
<!-- 下拉框 -->
<select name="sel" size="3" multiple>
<option value="1">广州</option>
<option value="2">深圳</option>
<option selected value="3">山东</option>
<option value="4">北京</option>
</select>
</div>
<input type="submit" value="提交">
</form>
</div>
</body>
</html>
optgroup 下拉框分组功能
用optgroup标签包着option标签，optgroup label属性为组名
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="x-ua-compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Title</title>
</head>
<body>
<div>
<form action="http://www.baidu.com" method="get">
<div>
<!-- optgroup 下拉框分组功能 -->
<select name="city" size="5" multiple="multiple">
<optgroup label="广东省">
<option value="1">广州</option>
<option value="2">深圳</option>
</optgroup> <optgroup label="浙江省">
<option value="1">杭州</option>
<option value="2">温州</option>
</optgroup>
</select>
</div>
<input type="submit" value="提交">
</form>
</div>
</body>
</html>