获取class1元素下的class2元素
注意 dom取值中间是有空格的
<!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=1.0">
<title>Document</title>
<script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.js"></script>
</head>
<body>
<div class="class1">
<span class="class2">class2</span>
</div>
<script>
var value=$('.class1 .class2').text();
alert(value)
</script>
</body>
</html>
选择同时含有class1和class2的元素
注意获取dom时，选择器中间没有空格
<!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=1.0">
<title>Document</title>
<script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.js"></script>
</head>
<body>
<span class=" class1 class2">class2</span>
<script>
var value = $('.class1.class2').text();
alert(value)
</script>
</body>
</html>
选择class1或者class2的元素
注意dom中间是有逗号的
<!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=1.0">
<title>Document</title>
<script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.js"></script>
</head>
<body>
<span class=" class1 class2">1</span>
<span class=" class1 ">2</span>
<span class=" class2">3</span>
<script>
var value = $('.class1,.class2').length;
alert(value)
</script>
</body>
</html>
class前缀为pre的所有div的jquery对象
<!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=1.0">
<title>Document</title>
<script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.js"></script>
</head>
<body>
<span class="pre-1">1</span>
<span class=" 1-pre">2</span>
<span class=" class2">3</span>
<script>
var value = $("span[class^='pre']").length;
alert(value)
</script>
</body>
</html>
class后缀为class的dom
<!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=1.0">
<title>Document</title>
<script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.js"></script>
</head>
<body>
<span class="pre-1">1</span>
<span class=" 1-last">2</span>
<span class=" 2-pre">2</span>
<span class=" class2">3</span>
<script>
var value = $("span[class$='last']").length;
alert(value)
</script>
</body>
</html>
class中包含pre的dom
<!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=1.0">
<title>Document</title>
<script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.js"></script>
</head>
<body>
<span class="pre-1">1</span>
<span class=" 1-last">2</span>
<span class=" 2-pre">2</span>
<span class=" class2">3</span>
<script>
var value = $("span[class*='pre']").length;
alert(value)
</script>
</body>
</html>