jQuery什么更快:选择器或方法?

问题描述

假设我有$('mySelector:first');和$('mySelector').first();.哪种方法最有效?我查看了源代码，但仍然无法弄清楚.

Let's say I have $('mySelector:first'); and $('mySelector').first();. Which way is the most efficient? I looked in the source, but still couldn't figure it out.

在第一种情况下，jQuery会遍历每个项目，直到获得第一个:

It looks like in the first case jQuery goes through every item until gets the first one:

CHILD: function( elem, match ) {
        var type = match[1],
        node = elem;
        switch ( type ) {
            ...
         case "first":
          while ( (node = node.previousSibling) )  {
           if ( node.nodeType === 1 ) {
            return false;
           }
          }
          if ( type === "first" ) {
           return true;
          }
          node = elem;
                ...
        }
}

在第二种情况下，jQuery对集合进行了切片，但是我不确定它的效率如何:

In second case jQuery slices the collection, but I am not sure how efficient it is:

function first() {
  return this.eq( 0 );
};

function eq( i ) {
  return i === -1 ?
    this.slice( i ) :
    this.slice( i, +i + 1 );
};

推荐答案

当前接受的答案与，将:first和:eq(0)与.first()和.eq(0)进行比较.

The current accepted answer is not consistent with tests across many browsers comparing :first and :eq(0) to .first() and .eq(0).

对于当前的主要桌面浏览器:
$('foo').first()几乎是$('foo:first')

For the current major desktop browsers:
$('foo').first() is almost four times faster than $('foo:first')

如果要检查方法，请此处是测试及其当前结果.

If you want to inspect the methodology, here are the tests and their current results.

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