Hi @Kiththa,
Unfortunately, you cannot include JavaScript files to the FSM web client, not without changing the core \ baseline at least.
Alternatively, to perform address lookups against external services from the web client would in my view only be possible through the FSM App Server.
To accomplish this you could develop a custom MPM in FSM, which will perform the address lookup and return collection of rows.
This MPM can be invoked by client script from web client.
The user experience will likely be different comparing the pre-bundled drop script you’ve been referring too but these are the options available in the FSM web client.
Cheers,
Ruben