CSS 选择器 ul li a {...} vs ul >李>一个 {...}

2022-01-10 00:00:00 css-selectors css
  1. ul>有什么区别?李>CSS 中的 {...} 和 ul li a {...}?
  2. 哪个效率更高，为什么?

推荐答案

">" 是 子选择器

"" 是 后代选择器

区别在于后代可以是元素的子元素，也可以是元素的子元素的子元素，也可以是子元素的子元素的子元素ad inifinitum.

The difference is that a descendant can be a child of the element, or a child of a child of the element or a child of a child of a child ad inifinitum.

子元素只是直接包含在父元素中的元素:

A child element is simply one that is directly contained within the parent element:

<foo> <!-- parent -->
  <bar> <!-- child of foo, descendant of foo -->
    <baz> <!-- descendant of foo -->
    </baz>
  </bar>
</foo>

对于这个例子，foo * 将匹配 <bar> 和 <baz>，而 foo >* 只会匹配 <bar>.

for this example, foo * would match <bar> and <baz>, whereas foo > * would only match <bar>.

关于你的第二个问题:

哪个更高效，为什么?

我实际上不会回答这个问题，因为它与开发完全无关.CSS 渲染引擎的速度如此之快，几乎没有* 优化 CSS 选择器的理由，只需要使它们尽可能短.

I'm not actually going to answer this question as it's completely irrelevant to development. CSS rendering engines are so fast that there is almost never* a reason to optimize CSS selectors beyond making them as short as possible.

与其担心微优化，不如专注于编写对当前案例有意义的选择器.在为嵌套列表设置样式时，我经常使用 > 选择器，因为区分正在设置样式的列表级别很重要.

Instead of worrying about micro-optimizations, focus on writing selectors that make sense for the case at hand. I often use > selectors when styling nested lists, because it's important to distinguish which level of the list is being styled.

* 如果在渲染页面时确实是一个问题，那么你可能在页面上有太多元素，或者 CSS 太多.然后你必须运行一些测试来看看实际的问题是什么.

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