jQuery选择器与filter() [英] jQuery selector vs filter()

问题描述

给出以下标记

<ul class="list">
    <li>first item</li>
    ​<li class="item">second item</li>
    <li>third item</li>
</ul>​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

这两个表达式中的哪一个最好选择第二个li?

Which one these 2 expressions is better to select the second li?

$("ul li.item")

或

$("ul li").filter(".item")

这不是一个很好的例子，因为它太简单了(我知道我可以做$(".item")，但是总的来说，我应该使用复杂的选择器还是过滤器功能?

This is not a very good example because it's too simple (I know I could be doing $(".item"), but in general, should I be using complex selectors or the filter function?

编辑:如果第一个效率更高，什么时候/最好使用过滤器功能?

EDIT: If the first is more efficient, when is it appropriate / best to use the filter function?

推荐答案

第一个更快:

$("ul li.item")

这是完全正确的，因为它是等效的，但是没有两次运行选择器引擎(Sizzle)才能到达那里.

This is true simply because it's equivalent, but isn't running the selector engine (Sizzle) twice to get there.

用于您使用 .filter() ...好，当您需要过滤当前集合时，或者当您需要复杂的过滤器时.例如，如果您想链接但不想再次选择集合:

For your edit: You use .filter()...well, when you need to filter the current set, or when you need a complex filter. For example if you wanted to chain but not select the set again:

$("ul li").addClass('everyItem').filter('.item').fadeOut();

或者是复杂的过滤器:

$("ul li").filter(function() {
  return $.data(this, 'hasSomething');
}).fadeOut();

很多用途的过滤器，实际上取决于哪种情况最适合.就像您的问题一样，$(selector).filter(selector) ...我想不出您是否希望在单个选择器上使用它，如果可能的话.在我头顶上唯一无法完成的情况是 :has() 和 :not() 包装.

There are many uses of filter, it really depends on the situation as to what fits best. As pertains to your question though, $(selector).filter(selector)...I can't think of a case where you'd want this over a single selector if it's at all possible. The only case off the top of my head you can't do that is a complex :has() and :not() wrapping.

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