ABCs of jQuery

Dipal Choksi
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In this article, we take an introductory look at the various components of jQuery.

What is it

JQuery is a JavaScript library that simplifies javascript programming.

In their own words, as quoted on the jQuery.com website - "jQuery is a fast and concise JavaScript Library that simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development."

Why do I need to know about it

Whether you work with Asp.net or SharePoint or any other web technologies, chances are that JQuery will be available to make life easier and your site user-friendly, more appealing and functionally rich.

Short and Simple overview

To describe what you can do with jQuery in a single line, the essence is that you select DOM elements and you manipulate them. Majority of jQuery core consists of selectors to easily find/reference DOM elements and events which enable manipulation of the DOM elements in your code.

First and foremost, you need a reference to the jquery library which can either be downloaded to your server and referenced or you can reference the jquery library available on the major CDNs which are free and available for public use.

You just need to reference this jquery.js library to start using the jQuery APIs.

Next, in your code, the most common task is to access the DOM elements. To ensure this occurs after the document is ready, we register a ready event for the document.

Selectors

jQuery offers a wide range of selectors - these tools enable you to select one or more DOM elements matching your criteria. I feel this is the heart of jQuery. Everything you do gets driven from this point. Various choices of selector elments are available to match every need. Some examples are

Select all button elements
Select all elements of class "heading"
Select an element with name=Author
Select all elements where <attribute> begins with <value>

And so on

Hierarchical selectors allow you to traverse parent/child/siblings etc.

Events

Events enable you to take action on selected elements in reaction to user interaction or system occurences. If selectors are the heart of jQuery, events are the soul :) All the action is in the events. Several events are available for use such as click, focus, bind, keyup etc.

Example

In the following code sample, we are going to attach a click event to all the anchor tags in the document - the event will basically display an alert message to the user before the navigating. Note the selector will register the event to all of the anchor tags. Also, note that I am using a public CDN instead of hosting jQuery locally. (There are pros and cons for both approaches, local as well as CDN)

<!DOCTYPE html>
 <html lang="en">
 <head>
   <meta charset="utf-8">
   <title>jQuery demo</title>
 </head>
 <body>
   <a href="http://www.microsoft.com/">Microsoft</a>
   <a href="http://www.yahoo.com/">Yahoo</a>
   <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.5/jquery.min.js"></script>
   <script>
     $(document).ready(function(){
       $("a").click(function(event){
         alert("You are now leaving this website");
       });
     });
   </script>
 </body>
 </html>

Code: Save as jq.html and open it in your browser to see it run.

Some browsers may pose a confirmation to the user. If you are prompted, click yes to allow blocked content.

Image: Sample in action

Plugins

A large system of plug-ins is available. you can have a choice of plug-ins for tables, calendars, tooltips, template engine, progress bars etc. The system of plug-ins makes the jQuery architecture extend to include new features.

You can use the vast pool of resources that is available and if you want, you can also author your own plug-ins.

Incidentally, at the time of writing this article, the plug-ins site is being revamped. You can follow the progress on GitHub https://github.com/jquery/plugins.jquery.com

Resources

JQuery Project - http://jquery.org/
jQuery Project manages all of teh JQuery projects including jQuery code, jQuery UI, Sizzle and QUnit

jQuery - http://jquery.com

jQuery UI - http://jqueryui.com/

jQuery Mobile - http://jquerymobile.com/

Discussion Forum - http://docs.jquery.com/Discussion

Twitter - twitter.com/jQuery

Documentation - http://docs.jquery.com

More to explore

jQuery UI

Definition from the jQuery UI site:

"jQuery UI provides abstractions for low-level interaction and animation, advanced effects and high-level, themeable widgets, built on top of the jQuery JavaScript Library, that you can use to build highly interactive web applications."

jQuery Mobile

As defined on the jQuery Mobile site:

A unified, HTML5-based user interface system for all popular mobile device platforms, built on the rock-solid jQuery and jQuery UI foundation.

Conclusion

In this article we explored the basics of jQuery and took a glimpse at it's working. We also got to know a little bit about it's advanced capabilities and resources where to look for, when you are ready to take this to the next level in your daily life.

Happy Coding!

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