JQuery, prototype, scriptalicious, moo tools and Microsoft Ajax are all JavaScript libraries that encapsulate common functionality, or rather commonly repeated tasks, into a re-usable form. One such example is accessing DOM elements. Usually you would type document.getElementById to get to a div element for example, which also implies for each element you access you have to type document.getElementById. Most JavaScript libraries provide an easy way to access elements, usually through a dollar($). In jQuery you simply type $(‘elementID’) and in Microsoft Ajax you type $get(‘elementID’) to get to the object. So basically the library has encapsulated the document.getElementById in some JavaScript function, and that function simply returns the object. Most JavaScript libraries also provide built-in AJAX functionality, which means that the library makes it easy to create XMLHTTPRequests. The libraries also make it easy to do all kinds of special effects such as animations and modal popups.

So which one do you use? What determines which one you use? Well personally I would take a pragmatic approach and say that no matter which library you choose, you still have to learn the basic concepts such as how HTTP requests work and how things are executed. Once these things are understood you can pick a library and make sure you learn it. Whether you pick jQuery or Microsoft Ajax is irrelevant, because with both you will have to spend time learning how the API works. I often find myself in a situation where I want to jump between libraries because I feel that there is a wow feature in the one and not the other. I also find myself creating my own JavaScript at times because I just don’t need the entire library. The most important thing to know though is that you have to commit your time and energy to learning JavaScript with or without the use of a library.