Using the XMLHttpRequest object in synchronous mode causes the entire browser to lock until the remote call completes. This is usually not a desirable behavior. The jQuery BlockUI Plugin lets you simulate synchronous behavior when using AJAX, without locking the browser.
When activated, it will prevent user activity with the page (or part of the page) until it is deactivated. BlockUI is useful for creating loading screen for web application. This is done by adding elements to the DOM to give it both the appearance and behavior of blocking user interaction.
jQuery BlockUI Plugin Examples
jQuery BlockUI Plugin is compatible with jQuery v1.2.3 and later and compatible with all major browsers.
Thanks sir BlockUI is a very useful thinks for me.