Is there a way in JS API to take an existing Map Service and Join it to another data source? Table, DBF etc.
Anyone have any examples if this is possible.
Sort of an on the fly tabular join to a Map Service.
I have personal experience setting-up a map to join a service to JSON data. There's also an example for this on ESRI's demo site:
Gas price data by state mashup | ArcGIS API for JavaScript
The data doesn't come from APIfy in the example... it's using the fallback, which is located here:
http://developers.arcgis.com/javascript/samples/data_gas_prices/fallback-gas-price-data.json
Just so you are aware, though, if you join your map to JSON data, you can create choropleths, legends, etc., but if you use the print widget and send the legend layer, it doesn't quite work right. I have an open ticket with ESRI for a workaround; there's also a thread: