Once an inbound or outbound call is in an established state, you can access a set of supplementary services. To access these services, you'll need the Call object, which is created when a call is initialized. Refer to Inbound/Outbound Calls for information on creating a Call object.

The Call object exposes the following supplementary service methods:

• doHoldResume()
• completeTransfer()
• sendDigit()

anchordoHoldResume Method

The doHoldResume() method puts the call on hold or resumes based on the current state of the call. If the call is connected, it's put on hold. Likewise if the call is already on hold, doHoldResume() resumes the call.

// Assuming the call(inbound/outbound) is already established and we have the call instance.

call.doHoldResume(); // call is put on hold

call.doHoldResume(); // call is resumed

You'll want to create a listener for the held event on the Call object to monitor the hold status of the call:

call.on('held', (callId: CallId) => {
  // Add code to handle successful hold
});

If the hold action is not successful, the Call object emits a hold_error event:

call.on('hold_error', (error: CallError) => {
  // Add code to handle hold error
});

If a call is resumed from hold successfully, the Call object emits a resumed event:

call.on('resumed', (callId: CallId) => {
  // Add code to handle successful resume
});

if the call is not resumed successfully, the Call object emits a resume_error:

call.on('resume_error', (error: CallError) => {
  // Add code to handle resume error
});

anchorcompleteTransfer Method

The completeTransfer() method initiate call transfers. The Calling SDK supports two types of transfers: blind transfer and a consult transfer.

The method accepts three arguments:

• transferType
• transferCallID
• transferTarget

The following table provides more details:

Blind Transfer

A blind transfer involves transferring a call to a destination without first consulting with the person to whom the call is being transferred. To initiate a blind transfer, set the transferType to BLIND and provide the transferTarget. For a blind transfer, transferTarget is mandatory. A transferCallId is not required for a blind transfer.

const call = line.makeCall();
const destination = '123456789';
// Note: transferCallId is used for consult transfer, and must be undefined for a blind transfer.
call.completeTransfer(TransferType.BLIND, undefined, destination); 

Consult Transfer

A consult transfer involves consulting with a new user before transferring the call to them. To initiate a consult transfer, set the transferType to CONSULT and provide the transferCallId. For a consult transfer, transferCallId is a mandatory argument. transferTarget is not required for a consult transfer.

Here's the workflow for a typical consult transfer:

1. UserA calls UserB. At this point, either of the users can transfer the call.
2. UserB wants to transfer the call. UserB will first have to put UserA on hold.
3. Now UserB will be able to dial out to UserC.
4. Once UserC answers, UserB and UserC will be in a connected call while UserA is on hold.
5. The completeTransfer() method can be invoked to allow UserB to transfer the call.
6. The CallId between UserA and UserB is the transferCallId and is passed to the method.
7. If the transfer is successful, UserA and UserC will be on a call and UserB will get disconnected from both the calls.

// callAB -> call between UserA and UserB
// callBC -> call between UserB and UserC

// UserA calls UserB
const callAB = line.makeCall();

// UserB puts UserA on hold
callAB.doHoldResume();

// UserB calls UserC
const callBC = line.makeCall();

// UserB completes the transfer
callAB.completeTransfer(TransferType.CONSULT, CallBC.getCallId());

If transfer is not successful, the CAll object emits a 'transfer_error' event.

call.on('transfer_error', (error: CallError) => {
  // Add code to handle transfer error
});

The CallError object contains the following members:

anchorsendDigit Method

The sendDigit() method sends a single DTMF digit on an established call which is useful, for instance, when navigating an Interactive Voice Response (IVR) system where a user is expected to enter a touch tone corresponding to menu item.

The method accepts a string representing the DTMF digit as a parameter:

const call = line.makeCall();
call.sendDigit('1');