What does the jQuery() function do?

In continuation to the question https://stackoverflow.com/questions/1452380/good-jquery-interview-questions-closed

I have a follow up question. Wh开发者_如何学运维at does the jQuery() function do? (there are four answer to this; subject should at least describe the selector-and-element-set mode)

I tried with googling but could not get a clear answer.

Thanks for any help in advance.

The jQuery function can handle several types of input:

• $(""), $(null), or $(undefined)
• $(DOMElement)
• $(html) -> $(array)
• $("#id")
• $("TAG")
• $(expr, $(...))
• $(expr, context)
• $(function)

Take a look at the source code of jQuery and jQuery.fn.init respectively to see how these are handled.

It does different things depending on what you pass to it:

jQuery(String query [, DOMElement context])
jQuery(String query [, jQueryResultSet context])

This will read the string as a query (eg: #foo > .bar a). It will be run in the context of context if it is specified, otherwise it is taken from document.

jQuery(DOMElement node)

This converts the node into a jQuery result set containing that node. This is used mostly when you have a reference to an element (eg: in an event handler) and you wish to perform jQuery functions upon it.

jQuery(Function readyHandler)

This is a shortcut form of this:

jQuery(document).ready(Function readyHandler)

Running all your jQuery functions once the document has been loaded is so common, this shortcut was added.

jQuery('')
jQuery(null)

This selects the document.

Have a look at this article, it might help you: http://simonwillison.net/2007/Aug/15/jquery/ Particularly, look at the "Doing stuff with them" paragraph.

All in this document : http://docs.jquery.com/Core