This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

The RTCPeerConnection.onicegatheringstatechange property is an EventHandler which specifies a function to be called when the icegatheringstatechange event is sent to an RTCPeerConnection instance. This happens when the ICE gathering state—that is, whether or not the ICE agent is actively gathering candidates—changes.

You don't need to watch for this event unless you have specific reasons to want to closely monitor the state of ICE gathering.


RTCPeerConnection.onicegatheringstatechange = eventHandler;


A function you provide which is passed a single parameter: an Event object containing the icegatheringstatechange event. You can determine the new state of ICE gathering by looking at the value of the RTCPeerConnection.iceGatheringState property.


This example updates status information presented to the user to let them know what's happening by examining the current value of the iceGatheringState property each time it changes and changing the contents of a status display based on the new information.

The status is simply presented as text in a <div> element:

<div id="iceStatus"></div>

The actual event handler looks like this:

pc.onicegatheringstatechange = function() {
  let label = "Unknown";

  switch(pc.iceGatheringState) {
    case "new":
    case "complete":
      label = "Idle";
    case "gathering":
      label = "Determining route";

  document.getElementById("iceStatus").innerHTML = label;


Specification Status Comment
WebRTC 1.0: Real-time Communication Between Browser
The definition of 'RTCPeerConnection.onicegatheringstatechange' in that specification.
Working Draft Initial specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support No support No support No support No support No support
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support No support No support No support No support No support

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

Event Handler ICE onicegatheringstatechange Property Reference RTCPeerConnection WebRTC