缓存或不缓存jQuery中的$（this） [英] To cache or not to cache $(this) in jQuery

问题描述

当选择器 $（this）时，创建和重用引用是否会显着提高性能？

Does creating and reusing a reference increase performance appreciably when the selector is $(this)?

I当我在同一范围内多次使用相同的选择器时，为我的jQuery选择器创建引用。以下更有效

I create references for my jQuery selectors when I use the same selector multiple times in the same scope. The following is more efficient

    var jSel = $('div.some_class input.some_other_class');
    some_function1(jSel);
    some_function2(jSel);

比这个

    some_function1($('div.some_class input.some_other_class'));
    some_function2($('div.some_class input.some_other_class'));

但是如果选择器只是 $（this）其中这个是jQuery方法中的dom元素。我是否需要创建对 $（this）的引用并重用该引用，或者我可以创建多个 $（this）选择器并期望获得类似的表现？

But what if the selector is simply $(this) where this is a dom element inside a jQuery method. Should I bother to create a reference to $(this) and reuse the reference or can I create multiple $(this) selectors and expect similar performance?

以下是

    var jSel = $(this);
    some_function1(jSel);
    some_function2(jSel);

明显快于以下情况？

    some_function1($(this));
    some_function2($(this));

推荐答案

以下是显着的比以下更快？

Is the following significantly faster than the following?

否。它在显微镜下更快;在几微秒的范围内。

No. It is microscopically faster; in the realms of just a few microseconds.

这是否会阻止您将结果分配给变量并使用它？ 否即可。使用变量可以为这个提供更多含义，并且可以更容易输入。另外，如果你不想在 $（this）上操作，而是想要 $（this）.next（），你必须在一个地方改变它而不是 n 。

Does that stop you assigning the result to a variable and using that? No. Using a variable can give more meaning to what this is, and can be easier to type. Plus, if you stopped wanting to operate on $(this), and instead wanted $(this).next(), you have to change it in one place instead of n.

你会发现jQuery构造函数是高度已经过优化，可以接受单个DOM元素作为参数。以下是执行的确切代码当你打电话给 $（DOMElement）（创建jQuery对象后，当然）：

You'll find the jQuery constructor is highly optimized for accepting a single DOM element as a parameter. The following is the exact code that gets executed when you call $(DOMElement) (after the jQuery object has been created, of course):

var match, elem, ret, doc;

// Handle $(""), $(null), or $(undefined)
if ( !selector ) {
    return this;
}

// Handle $(DOMElement)
if ( selector.nodeType ) {
     this.context = this[0] = selector;
    this.length = 1;
    return this;
}

// Handle lots of other param types, but we hit the above one, so we've stopped now...

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