*真的有多慢？ [英] How slow is * really?

问题描述

每个人都说， * {...} 选择器非常慢。但是它真的有多慢？

Everybody states, that the * { ... } selector is very slow. But how slow is it really?

我总是试图避免它，但有时它是非常有用的。例如： * + h1 {margin-top 1em; } c>




I always try to avoid it, but sometimes it's very useful. For example: * + h1 { margin-top 1em; }

推荐答案

/ code>只有您网页上有元素才会慢。

To put it very simply: the universal selector * is only as slow as there are elements on your page.

由于从右到左匹配的浏览器接受每个元素并匹配所有候选规则，将匹配 * 很好。它本身不会损害性能，但如果你有很多元素在您的页面或一个非常复杂的DOM，这是据称它变慢，但即使这样也不会明显降低浏览器性能。

Since right-to-left matching browsers take each element and match it against all candidate rules, every element will match * just fine. It by itself doesn't harm performance, but if you have many elements in your page or a very complex DOM, that's where it allegedly gets slow, but even then it doesn't visibly degrade browser performance.

例如， * + h1 是合理的，因为如果你想考虑匹配的性能， -left匹配浏览器将首先在 h1 元素上测试该选择器，然后检查是否有任何元素出现在它们之前（这真的不需要花费太多的精力，因为 * 基本上是一个保证的匹配）。

Even something like * + h1, for example, is reasonable, since if you want to take matching performance into account, then a right-to-left matching browser will test that selector only on h1 elements first, before checking if there's any element occurring before them (which really doesn't take much effort as * is basically a guaranteed match).

您还可以查看这个我的答案到类似的问题 * + * （这是两个通用选择器！）。

You may also wish to check out this answer of mine to a similar question about * + * (that's two universal selectors!).

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