The $() factory function: in JQuery

All type of selectors available in jQuery, always start with the dollar sign and parentheses: $().

The factory function $() makes use of following three building blocks while selecting elements in a given document:

jQuery	Description
Tag Name:	Represents a tag name available in the DOM. For example $('p')selects all paragraphs in the document.
Tag ID:	Represents a tag available with the given ID in the DOM. For example$('#some-id') selects the single element in the document that has an ID of some-id.
Tag Class:	Represents a tag available with the given class in the DOM. For example $('.some-class') selects all elements in the document that have a class of some-class.

All the above items can be used either on their own or in combination with other selectors. All the jQuery selectors are based on the same principle except some tweaking.

NOTE: The factory function $() is a synonym of jQuery() function. So in case you are using any other JavaScript library where $ sign is conflicting with some thing else then you can replace $sign by jQuery name and you can use function jQuery() instead of $().

The Document Ready Event in JQuery

You might have noticed that all jQuery methods in our examples, are inside a document ready event:

$(document).ready(function(){
// jQuery methods go here...
});
This is to prevent any jQuery code from running before the document is finished loading (is ready).

It is good practice to wait for the document to be fully loaded and ready before working with it. This also allows you to have your JavaScript code before the body of your document, in the head section.

Here are some examples of actions that can fail if methods are run before the document is fully loaded:
Trying to hide an element that is not created yet
Trying to get the size of an image that is not loaded yet

Tip: The jQuery team has also created an even shorter method for the document ready event:

$(function(){
// jQuery methods go here...
});
Use the syntax you prefer. We think that the document ready event is easier to understand when reading the code.

How to use JQuery library

Here we can see that how to use JQuery in our HTML Page. If you don't want to download and host jQuery yourself, you can include it from a CDN (Content Delivery Network). Both Google and Microsoft host jQuery. To use jQuery from Google or Microsoft, use one of the following in alternate downloading: