Managing an FVTerm Child iFrame in Javascript

In msgAPI mode this replaces what can be used in FVTermParent with the fvApi.fvWin.SetTermFocus() call.

Since in the messaging environment access to the FVTerm window calls are not available, this was implemented using messaging.

This returns a Promise so if you wish to now if the FVTerm emulator has focus at the completion of the call, use an await as follows:

var hasFocus = await fvApi.SetTermFocus();