onCall
Register the inbound call handler. The provided function is called once for each
calling.call.receive event on the subscribed contexts. The function receives a
Call object with all call properties
and control methods.
Only one call handler can be active at a time. Calling onCall() again replaces
the previous handler.
Parameters
handler
An async function that receives a Call object. Signature:
(call: Call) => void | Promise<void>.
Returns
void