The read-only RTCErrorEvent property error contains an RTCError object describing the details of the error which the event is announcing.

An RTCError object whose properties provide details about the error which has occurred in the context of a WebRTC operation.

In this example, a handler is established for an RTCDataChannel's error event.

dataChannel.addEventListener("error", (event) => {
  let error = event.error;

  if (error.errorDetail === "sdp-syntax-error") {
    let errLine = error.sdpLineNumber;
    let errMessage = error.message;

    let alertMessage = `A syntax error occurred interpreting line ${errLine} of the SDP: ${errMessage}`;
    showMyAlertMessage("Data Channel Error", alertMessage);
  } else {
    terminateMyConnection();
  }
});

If the error is an SDP syntax error—indicated by its errorDetail property being sdp-syntax-error—, a message string is constructed to present the error message and the line number within the SDP at which the error occurred. This message is then displayed using a function called showMyAlertMessage(), which stands in for whatever output mechanism this code might use.

Any other error is treated as terminal, causing a terminateMyConnection() function to be called.

The above example uses addEventListener() to add the handler for error events. You can also use the RTCDataChannel object's onerror event handler property, like this:

dataChannel.onerror = (event) => {
  let error = event.error;

  /* and so forth */
};