Hi Bandid,
Since you're planning on using JavaScript rather than Silverlight, we can focus entirely on the server side of things. The two following links should be helpful. They show the REST API as it currently exists at ArcFM Server 10.0.3, and the planned changes for 10.1 (as you can see, there are not many - and only client-side). Since ArcFM Server 10.1 is primarily a compatibility release to work with ArcGIS Server 10.1, REST should mostly be the same, and you can probably begin against a 10.0.3 server.
REST APIWhat's new in ArcFM Server (you'll need to scroll down to the 'ArcFM Server' section since the page doesn't appear to have anchors)