是：last-child选择器性能不好吗？ [英] Is the :last-child selector bad for performance?

问题描述

我使用：last-child 选择器很多次，主要是在列表中使用 border-bottom 我使用 border：none; 为最后一个孩子，或当使用边距。所以我的问题是，从性能角度来看，：last-child 选择器坏吗？

I use :last-child selector plenty of times, mostly when using border-bottom in a list where I use border: none; for the last child, or when using margins. So my question is, is the :last-child selector bad from a performance point of view?

听说它从CSS2规范中删除，因为使用：first-child 很容易让浏览器检测，但是检测：last-

Also I've heard that it was removed from the CSS2 specification because using :first-child is easy for the browser to detect, but for detecting :last-child it needs to loop back.

推荐答案

如果由于性能问题而从CSS2延迟，

If it was deferred from CSS2 for performance concerns, but reintroduced in Selectors 3, I suspect that it's because performance is no longer an issue as it previously was.

请记住，：last-child

Remember that :last-child is the definitive and only way to select the last child of a parent (besides :nth-last-child(1), obviously). If browser implementers no longer have performance concerns, neither should we as authors.

我可以想到的唯一令人信服的原因是覆盖边框样式 ：first-child 而不是：last-child 是允许与IE7和IE8兼容。如果这提高了性能，让这是一个副作用。如果您不需要 IE7和IE8支持，那么您不应该感到被迫使用：first-child over ：last-child 。即使浏览器的性能是绝对关键，你应该通过测试和基准测试正确的方式，而不是过早的优化。

The only compelling reason I can think of for overriding a border style with :first-child as opposed to :last-child is to allow compatibility with IE7 and IE8. If that boosts performance, let that be a side effect. If you don't need IE7 and IE8 support, then you shouldn't feel compelled to use :first-child over :last-child. Even if browser performance is absolutely critical, you should be addressing it the proper way by testing and benchmarking, not by premature optimization.

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