The Microsoft AJAX Client-side library is now split up across multiple JavaScript files – allowing you to download and use only those script files that you actually need (reducing download sizes). 

Manually adding all of the script files required to use Ajax controls can be tedious though (and error prone). To make it easier to use both client controls as well individual client library components, we are introducing a new client script loader with today’s release. This client script loader helps you automatically load all of the scripts required by a control and execute the scripts in the right order when a page loads.

For example, the following page uses the client script loader to load all of the scripts required by the “watermark” control, and then wires up the watermark control to an <input> textbox:

Figure 7

Notice the call to the Sys.require() method above. When you call Sys.require(), you supply the name of a client component (or an array of client components) that you want to load. The sys.require() client loader then automatically downloads all of the required script files in parallel (allowing your scripts to load faster and also allow you to avoid blocking the page from rendering).  When all of the scripts required by the components requested are loaded, the Sys.onReady() method is called and the watermark is created.

Above we are binding the “watermark” control to a <input> textbox with an id of “name”.  At runtime the watermark control will cause the textbox to have a watermark (that automatically disappears when a user sets the focus on the textbox and starts typing):

Figure 8

The client script loader supports many advanced features including automatic script combining and lazy loading. It can also be smart about downloading either debug or release versions of libraries. It also allows you to register your own libraries and have them automatically be loaded as well using the Sys.require() syntax.