参考文章：https://zhidao.baidu.com/question/120064132.html
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文章目录
HTML div标签的class属性
HTML (HyperText Markup Language)是用于创建网页的标准标记语言。它使用标签来描述网页的各个部分。其中，div标签常被用作网页布局和样式设计的容器，而class属性则在控制这些元素的样式和行为方面发挥着重要的作用。
1. class属性的基本定义和用途
class属性是一种全局属性，可用于任何HTML元素。其主要目的是为元素提供一个或多个类名，这些类名可以在CSS中引用，以添加样式，或者在JavaScript中引用，以操纵元素。
例如，在CSS中，我们可以通过.classname选择器来应用样式：
<div class="red-text">Hello, World!</div>
.red-text {
color: red;
}
在这个例子中，所有具有"class=red-text"的元素都会显示为红色文字。
2. class属性的特性
2.1 可复用性
不同的元素可以共享相同的类名，从而实现样式的复用。例如：
<div class="red-text">Hello</div>
<p class="red-text">World</p>
在这个例子中，div和p元素都共享了"red-text"类，因此他们的文字颜色都会被设置为红色。
2.2 多类名
一个元素可以有多个类名，类名之间用空格分隔。例如：
<div class="red-text large-font">Hello, World!</div>
.red-text {
color: red;
}
.large-font {
font-size: 24px;
}
在这个例子中，div元素同时拥有"red-text"和"large-font"两个类，因此它的文字颜色为红色，且字体大小为24px。
2.3 CSS选择器优先级
当一个元素同时拥有多个类时，如果这些类的样式发生冲突，那么在CSS中最后定义的类将会优先应用。例如：
<div class="red-text blue-text">Hello, World!</div>
.red-text {
color: red;
}
.blue-text {
color: blue;
}
在这个例子中，由于"blue-text"类在CSS中的位置在"red-text"之后，因此div元素的文字颜色将会是蓝色。
3. 在JavaScript中使用class
除了在CSS中应用样式外，class属性还可以在JavaScript中用于操作元素。例如，我们可以使用document.getElementsByClassName()方法来获取所有具有指定类名的元素：
let elements = document.getElementsByClassName("red-text");
在这个例子中，elements变量将包含所有具有"red-text"类的元素。
参考文章：MDN Web Docs - class
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