How do I use JavaScript to query the CRM database in 2011?

Hi,

I'm using CRM 2011 on Rollup 10.

I'm looking to automatically populate the Opportunity form both onload (of the form) and onchange of a particular field.

So, I have a field, let's call it FieldA, which is a text field.  When I enter data into this field I want to automatically populate a number of other fields if there is a match already in the database with the data that has been entered into this field.  The information populated should match a pre-existing opportunity which has the same information as that contained in FieldA.

The fields I want to populate include customerid, and a number of other lookups and dropdowns (let's call these, FieldB, FieldC, FieldD, and FieldE).

What is the best/easiest way to achieve this?

Any help would be greatly appreciated.

Thanks,

Matt.