RTCPeerConnection.onsignalingstatechange

The onsignalingstatechange event handler property of the RTCPeerConnection interface specifies a function to be called when the signalingstatechange event occurs on an RTCPeerConnection interface. The function receives as input the event object of type Event; this event is sent when the peer connection's signalingState changes, which may happen either because of a call to setLocalDescription() or to setRemoteDescription().

rtcPeerConnection.onsignalingstatechange = errorHandler;

Set this to a function which you provide that receives an Event object as input; this contains the signalingstatechange event. This event object doesn't provide details about what changed, but you can examine the signalingState property to determine what the new state is.

You may also, as always, set up a handler for the signalingstatechange event using addEventListener():

myRTCPeerConnection.addEventListener("signalingstatechange", mySignalingStateChangeHandler);

Or, using an anonymous (inline) handler:

myRTCPeerConnection.addEventListener("signalingstatechange", event => {
  /* handle the event here */
});

This snippet shows a handler for signalingstatechange that looks for the "have-local-pranswer" signaling state—indicating that a remote offer has been received and a local description of type "pranswer" has been applied in response.

pc.onsignalingstatechange = function(event) {
  if (pc.signalingState === "have-local-pranswer") {
    // setLocalDescription() has been called with an answer
  }
};

• Signaling and video calling: A WebRTC example
• The signalingstatechange event and its type, Event.