id 和 class 有什么区别? [英] What's the difference between an id and a class?

问题描述

<div class=""> 和 <div id=""> 在 CSS 方面有什么区别?用<div id="">可以吗?

What's the difference between <div class=""> and <div id=""> when it comes to CSS? Is it alright to use <div id="">?

我看到不同的开发人员以两种方式这样做，而且由于我是自学的，所以我从来没有真正弄明白过.

I see different developers doing this in both ways, and since I'm self taught, I've never really figured it out.

推荐答案

ids 必须是唯一的，因为 class 可以应用于很多事情.在 CSS 中，ids 看起来像 #elementID 而 class 元素看起来像 .someClass

ids must be unique where as class can be applied to many things. In CSS, ids look like #elementID and class elements look like .someClass

通常，当您想引用特定元素时使用 id，而当您有许多相似的东西时，请使用 class.例如，常见的 id 元素是诸如 header、footer、sidebar 之类的东西.常见的 class 元素是诸如 highlight 或 external-link 之类的东西.

In general, use id whenever you want to refer to a specific element and class when you have a number of things that are all alike. For instance, common id elements are things like header, footer, sidebar. Common class elements are things like highlight or external-link.

阅读级联并了解分配给各种选择器的优先级是个好主意:http://www.w3.org/TR/CSS2/cascade.html

It's a good idea to read up on the cascade and understand the precedence assigned to various selectors: http://www.w3.org/TR/CSS2/cascade.html

然而，您应该了解的最基本的优先级是 id 选择器优先于 class 选择器.如果你有这个:

The most basic precedence you should understand, however, is that id selectors take precedence over class selectors. If you had this:

<p id="intro" class="foo">Hello!</p>

和:

#intro { color: red }
.foo { color: blue }

文本会是红色的，因为 id 选择器优先于 class 选择器.

The text would be red because the id selector takes precedence over the class selector.

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