What does $(''class for the same element', element) mean?

I don't unterstand this syntax:

var dir = $("a.store").parents("tab开发者_StackOverflow中文版le")[0];
var stores = $("a.store:has(b)", dir);

What will store contain?

What is the meaning of "$("a.store:has(b)", dir);"?

It will return a collection of dom elements that match the css selector ("a.store:has(b)") that are children of the dom element stored in the 'dir' variable.

In your example, dir is the context of the selector. From the docs linked by Felix in his comment:

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');
});

From the jquery docs,

:has() Selector

Selects elements which contain at least one element that matches the specified selector.

The expression $('div:has(p)') matches a <div> if a <p> exists anywhere among its descendants, not just as a direct child.

http://api.jquery.com/has-selector/

Regarding the second parameter to jQuery, it is the context. It can be a DOM element on which the selector operates.

In your case: var dir will have a table which is parent of <a class="store" ...

the store variable will contain only those <a class="store" .. which have a <b> inside them.

$("a.store")

Will get all <a> elements that have the class .store

.parents("table")[0];

Will get the table(s) these <a> reside in.

$("a.store:has(b)", dir);

Will find all <a> elements that have the class .store and contain a <b> element, using the previously found tables dir as context, meaning that instead of going through the entire document to find matches, it will only go through these tables.

In its simplest form..

Its equivalent to doing..

$('someParent').find('.matchingDescendants');