RTCPeerConnection.onnegotiationneeded

The RTCPeerConnection.onnegotiationneeded property is an EventHandler which specifies a function which is called to handle the negotiationneeded event when it occurs on an RTCPeerConnection instance. This event is fired when a change has occurred which requires session negotiation.

The most common scenario in which this will happen is at the beginning of a connection. After using createOffer() to create a new offer and setting it as the description of the local end of the connection by calling setLocalDescription(), the browser will, when it's ready, fire negotiationneeded to let you know it's ready for you to begin negotiating the connection. That's when it's time to send the offer along through the signaling server.

Syntax

RTCPeerConnection.onnegotiationneeded = eventHandler;

Value

This should be set to a function you provide which is passed a single parameter: an Event object containing the negotiationneeded event. There's no additional information provided in the event; anything you need, you can get by examining the properties of the RTCPeerConnection.

Example

This example, derived from the example in Signaling and video calling, establishes a handler for negotiationneeded events to handle creating an offer, configuring the local end of the connection, and sending the offer to the remote peer.

pc.onnegotiationneeded = function() {
  pc.createOffer().then(function(offer) {
    return pc.setLocalDescription(offer);
  })
  .then(function() {
      // Send the offer to the remote peer through the signaling server
    });
  })
  .catch(reportError);
}

First, it creates the offer by calling createOffer(). When that succeeds, the offer is passed into setLocalDescription() to set the local description for the connection. Once that's succeeded in turn, the offer can be sent to the signaling server for delivery to the remote peer.

Specifications

Browser compatibility

[1] Though this property is not prefixed, the RTCPeerConnection interface it belongs to was until Firefox 44.

See also

• The negotiationneeded event and its type, Event.