javascript - $() 的第二个参数是什么意思？

Question

我有一个jQuery代码如下；

var favorites       = $("#favorites");
var favoritesFooter = $("#favoritesFooter",favorites);

我不确定第二个语句中的逗号是什么意思 $("#favoritesFooter",favorites);

下面的语句在上述情况下会做什么或表示什么；

favoritesFooter.prev().after(newHTML);

Answer 1

它是 $() 的第二个参数。如 documentation 中所述:

Selector Context

By default, selectors perform their searches within the DOM starting at the document root. However, an alternate context can be given for the search by using the optional second parameter to the $() function. For example, to do a search within an event handler, the search can be restricted like so:

$('div.foo').click(function() {
  $('span', this).addClass('bar');
});

When the search for the span selector is restricted to the context of this, only spans within the clicked element will get the additional class.

Internally, selector context is implemented with the .find() method, so $('span', this) is equivalent to $(this).find('span').