The Microsoft AJAX library is a client-based JavaScript library that is compatible with all modern browsers and offers a lot of functionality as compared to JavaScript. This library is released with new features and fully supports ASP.NET 4.0'. The new features included in the Microsoft AJAX library are as follows:
Imperative syntax - Supports simple imperative syntax that is used to create and manage controls.
Script loader - Retrieves all scripts that are needed by one or more client component or control automatically and executes the scripts in the order in which they are received.
Client data access - Supports to access client data and display by client data control and client template.
Client datacontext - Supports read and write permission to data from a database.
The AdoNetDataContext class - Enables you to easily interact with an ADO.NET Data Services service.
jQuery integration - Helps to access the elements in your Web pages, work with client-side events, enable visual effects, and make it easier to use AJAX in your applications.