02 jQuery选择器
jQuery的逻辑和css选择器的逻辑是一样的.
// 语法: $(选择器)
可以使用jQuery选择器快速的对页面结构进行操作.
案例:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<script src="jquery.min.js"></script>
<script>
$(function(){
$(".btn").on('click', function(){
$(".info").text("");
let username = $("#username").val();
let password = $("#password").val();
let gender = $("input:radio[name='gender']:checked").val(); // input标签中radio 并且name是gender的. 并且被选择的.
let city = $("#city").val();
let flag = true;
if(!username){
$("#username_info").text('用户名不能为空!');
flag = false;
}
if(!password){
$("#password_info").text('密码不能为空!');
flag = false;
}
if(!gender){
$("#gender_info").text('请选择性别!');
flag = false;
}
if(!city){
$("#city_info").text('请选择城市!');
flag = false;
}
if(flag){
$("#login_form").submit();
} else {
return;
}
})
})
</script>
</head>
<body>
<form id="login_form">
<label for="username">用户名: </label><input type="text" id="username" name="username"><span class="info" id="username_info"></span><br/>
<label for="password">密码: </label><input type="password" id="password" name="password"><span class="info" id="password_info"></span><br/>
<label>性别: </label>
<input type="radio" id="gender_men" name="gender" value="men"><label for="gender_men">男</label>
<input type="radio" id="gender_women" name="gender" value="women"><label for="gender_women">女</label>
<span class="info" id="gender_info"></span>
<br/>
<label for="city">城市: </label>
<select id="city" name="city">
<option value="">请选择</option>
<option value="bj">北京</option>
<option value="sh">上海</option>
<option value="gz">广州</option>
<option value="sz">深圳</option>
</select>
<span class="info" id="city_info"></span>
<br/>
<input type="button" class="btn" value="登录">
</form>
</body>
</html>