Javascript 使用jQuery选择具有特定类的第一个和最后一个元素
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/4082600/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Select first and last element with particular class using jQuery
提问by tsusanka
I have a list of spans with particular class "place" and some of them have class "activated". Is there a way to select the first item with class "activated" and the last?
我有一个具有特定类“位置”的跨度列表，其中一些具有“激活”类。有没有办法选择“已激活”类的第一个项目和最后一个项目？
<span class="place" onclick="activate();">1</span>
<span class="place" onclick="activate();">2</span>
<span class="place activated" onclick="activate()">3</span>
<span class="place activated" onclick="activate();">4</span>
<span class="place activated" onclick="activate();">5</span>
<span class="place activated" onclick="activate();">6</span>
<span class="place" onclick="activate();">7</span>
回答by Stephen
var firstspan = $('span.activated:first'),
lastspan = $('span.activated:last');
By the way, if you're using jQuery, what's with all the inline click events?
顺便说一句，如果您使用的是 jQuery，那么所有内联点击事件有什么用？
You could add some code like so:
你可以像这样添加一些代码：
$('span.place').click(function() {
activate(); // you can add `this` as a parameter
// to activate if you need scope.
});
回答by Jordan Running
var places = $('span.place.activated');
var first = places.first(),
last = places.last();
Explanation: The span.places.activatedselector will get all <span>s with both "place" and "activated" classes. Then the first()and last()methods will return the first and last items of that set. This is preferable to using the :firstand :lastpseudoselectors because selection is expensive and this way we only do selection once and then rely on (cheap) array operations to get the first and last elements.
说明：span.places.activated选择器将获得所有<span>具有“位置”和“激活”类的 s。然后first()andlast()方法将返回该集合的第一个和最后一个项目。这比使用:first和:last伪选择器更可取，因为选择很昂贵，这样我们只进行一次选择，然后依靠（便宜的）数组操作来获取第一个和最后一个元素。
回答by Vasyl
If you take care about performance, than better use $('span.place.activated')instead $('.activated:first').
But, in this case, the second variant correct too.
如果你需要关心性能，优于使用$('span.place.activated')代替 $('.activated:first')。但是，在这种情况下，第二个变体也正确。
回答by Aaron Hathaway
var first = $('.activated:first');
var last = $('.activated:last');
