Hi Benarji
If you are working with Crm 2011 you can use the oData Service endpoint to query entity data from Javascript.
Here is a link to a thread with a similar question:
http://social.msdn.microsoft.com/Forums/de-DE/crmdevelopment/thread/8d57d177-f990-45b7-9a87-5d5e38dd0b9b
Use the CrmRestKit with jquery and JSON2 js libraries to build simple oData queries and update entities with javascript.
For further information for the oData filter syntax have a look at this website.
http://www.odata.org/developers/protocols/uri-conventions
For debugging I recommend you install Fiddler (http://fiddler2.com/fiddler2/) to see what URLs are created by the CrmRestKit and to track the HTTP traffic.
If you have any question or need further help just let me know.
hth
Uli