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Intermediate

The difference between synchronous and asynchronous PostBack is as follows:

  1. Asynchronous PostBack renders only the required part of the page; whereas, synchronous PostBack renders the entire page for any PostBack.
  2. Asynchronous PostBack executes only one PostBack at a time, that is, if you have two buttons doing asynchronous PostBack, the actions will be performed one by one; whereas, synchronous PostBack executes all the actions at once.
  3. Asynchronous PostBack only modifies the update panel that raises the PostBack; whereas, synchronous PostBack modifies the entire page.


JavaScript does not have threads. JavaScript functions are called when an event happens in a page such as the page is loaded, a mouse click, or a form element gains focus. You can create a timer using the setTimeout which takes a function name and time in milliseconds as arguments. 

Use the ScriptManager AsyncPostBackTimeout Property. For example, if you want to debug a web page but you get an error that the page request has timed out, you may set where the value specified is in seconds. 

Yes. But this has to be done before the init event of the page (or during runtime after the page has already loaded). Otherwise an InvalidOperationException will be thrown.

Dojo is a third-party javascript toolkit for creating rich featured applications. Dojo is an Open Source DHTML toolkit written in JavaScript. It builds on several contributed code bases (nWidgets, Burstlib, f(m)), which is why we refer to it sometimes as a "unified" toolkit. Dojo aims to solve some long-standing historical problems with DHTML which prevented mass adoption of dynamic web application development. 

From your JavaScript clients you can access data in other domains if the return data is provide in JSON format. In essence you can create a JavaScript client that runs operates using data from a different server. This technique is know as JSON with Padding or JSONP. There are questions as to whether this method is secure as you are retrieving data from outside your domain and allowing it to be excuted in the context of your domain. 
Not all data from third parties is accessible as JSON and in some cases you may want an extra level of protection. With Java you can provide a proxy to third party services using a web component such as a servlet. This proxy can manage the communication with a third party service and provide the data to your clients in a format of your choosing. You can also cache data at your proxy and reduce trips to service. For more on using a Java proxy to create mashups see The XmlHttpProxy Client for Java.

HTML_AJAX does not have specific plans to integrate with other JavaScript libraries. Part of this is because external dependencies make for a more complicated installation process. It might make sense to offer some optional dependencies on a library like scriptaculous automatically using its visual effects for the loading box or something, but there is not a lot to gain from making default visuals like that flashier since they are designed to be easily replaceable.

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