最合适的方式：$（$（“。answer”）[0]）

Suppose I want to get the first element amongst all the elements of the class ".answer"

假设我想获得“.answer”类中所有元素中的第一个元素

$($(".answer")[0])

I can do the above, but what is the best balance between elegance and speed?

我可以做到这一点，但优雅和速度之间的最佳平衡是什么？

*changed the question to reflect the current discussion

*改变了问题以反映当前的讨论

3 个解决方案

#1

The following are all equivalent in functionality (though not speed):

以下都是功能相同的（虽然不是速度）：

• var a0 = $($('.answer')[0]);
• var a0 = $（$（'。answer'）[0]）;
• var a0 = $('.answer').first(); - see http://api.jquery.com/first/
• var a0 = $（'。answer'）。first（）; - 见http://api.jquery.com/first/
• var a0 = $('.answer:first'); - see http://api.jquery.com/first-selector/
• var a0 = $（'。answer：first'）; - 见http://api.jquery.com/first-selector/
• var a0 = $('.answer').eq(0); - see http://api.jquery.com/eq/
• var a0 = $（'。answer'）。eq（0）; - 见http://api.jquery.com/eq/
• var a0 = $('.answer:eq(0)'); - see http://api.jquery.com/eq-selector/
• var a0 = $（'。answer：eq（0）'）; - 请参阅http://api.jquery.com/eq-selector/

Which is the best?
It has been hypothesized that the selector versions should be faster than the method versions (and the logic makes some sense) but I have not yet found a reliable cross-browser, multi-document benchmark that proves this to be true.

哪个最好？已经假设选择器版本应该比方法版本更快（并且逻辑有一定意义）但我还没有找到可靠的跨浏览器，多文档基准测试，证明这是真的。

And in some cases you cannot use the selector, as you have a jQuery object resulting from chained results and must later pare it down.

在某些情况下，您不能使用选择器，因为您有一个由链接结果产生的jQuery对象，并且必须在以后削减它。

Edit: Based on the excellent information from @yc's tests below, following are the current (2011-Feb-4) test results summarized and compared against a baseline of .answer:first:

编辑：根据以下@ yc测试的优秀信息，以下是当前（2011年2月4日）测试结果的总结，并与.answer基线进行比较：首先：

          :first  :eq(0)  .first()  .eq(0)  $($('...')[0])
Chrome 8+   100%     92%      224%    266%       367%
   FF 3.6   100%    100%      277%    270%       309%
  FF 4.0b   100%    103%      537%    521%       643%
 Safari 5   100%     93%      349%    352%       467%
 Opera 11   100%    103%      373%    374%       465%
     IE 8   100%    101%     1130%   1246%      1767%
 iPhone 4   100%     95%      269%    316%       403%
=====================================================
 Weighted   100%     92%      286%    295%       405%
    Major   100%     95%      258%    280%       366%

• The Weighted line shows the performance weighted by the number of tests per browser; popular browsers (among those testing) are counted more strongly.
• 加权线显示每个浏览器的测试次数加权的性能;流行的浏览器（在那些测试中）被更强烈地计算。
• The Major line shows the same, only including non-beta releases of the major desktop browsers.
• Major系列显示相同，仅包括主要桌面浏览器的非beta版本。

In summary: the hypothesis is (currently) wrong. The methods are significantly faster than the Sizzle selectors, and with almost no exception the OP's code $($('.answer')[0]) is the fastest of them all!

总之：假设（目前）是错误的。这些方法明显快于Sizzle选择器，并且几乎没有例外，OP的代码$（$（'。answer'）[0]）是最快的！

#2

I can't speak to the elegance aspect, but the performance aspect here actually can make a huge difference.

我不能说优雅的方面，但这里的表现方面实际上可以产生巨大的差异。

It looks like, from a set of JavaScript testing, that your original method is actually the most efficient one, and contrary to the hypothesizing that the accepted answer linked to, non-CSS Sizzle selectors tend to be much less efficient than method selectors. There's a reason for that. The $('.answer') can use the browser native getElementsByClass() without having to manually traverse the results. The :first selector complicates that. In this instance, using the sizzle selectors seems to slow the selection by a factor of between 4-5.

看起来，从一组JavaScript测试中，您的原始方法实际上是最有效的方法，并且与假设所接受的答案相关联，非CSS Sizzle选择器往往比方法选择器效率低得多。这是有原因的。 $（'。answer'）可以使用浏览器本机getElementsByClass（），而无需手动遍历结果。 ：第一选择器使其复杂化。在这种情况下，使用嘶嘶声选择器似乎会使选择速度减慢4-5倍。

I'd argue that, with jQuery, performance should trump elegance, and all evidence (every single browser I've tested so far!) seems to indicate that OP's inelegant solution is the fastest by a fair amount.

我认为，使用jQuery，性能应该胜过优雅，所有证据（到目前为止我测试过的每一个浏览器！）似乎都表明OP的优雅解决方案是最快的。

Here are the results of the browsers with the most test runs:

以下是测试运行次数最多的浏览器的结果：

(The numbers are 'operations per second', so higher numbers are faster, lower numbers are slower.)

（这些数字是'每秒操作数'，所以数字越高，数字越慢。）

#3

Use the :first selector or the .first filter method:

使用：first selector或.first filter方法：

$(".answer:first");

or:

要么：

$(".answer").first();