The read-only RTCPeerConnection property canTrickleIceCandidates returns a boolean value which indicates whether or not the remote peer can accept trickled ICE candidates.
ICE trickling is the process of continuing to send candidates after the initial offer or answer has already been sent to the other peer.
This property is only set after having called RTCPeerConnection.setRemoteDescription(). Ideally, your signaling protocol provides a way to detect trickling support, so that you don't need to rely on this property. A WebRTC browser will always support trickle ICE. If trickling isn't supported, or you aren't able to tell, you can check for a falsy value for this property and then wait until the value of iceGatheringState changes to "completed" before creating and sending the initial offer. That way, the offer contains all of the candidates.
A boolean value that is true if the remote peer can accept trickled ICE candidates and false if it cannot. If no remote peer has been established, this value is null.
Note: This property's value is determined once the local peer has called RTCPeerConnection.setRemoteDescription(); the provided description is used by the ICE agent to determine whether or not the remote peer supports trickled ICE candidates.
const pc = new RTCPeerConnection();
function waitToCompleteIceGathering(pc) {
return new Promise((resolve) => {
pc.addEventListener(
"icegatheringstatechange",
(e) =>
e.target.iceGatheringState === "complete" &&
resolve(pc.localDescription),
);
});
}
async function newPeer(remoteOffer) {
await pc.setRemoteDescription(remoteOffer);
const offer = await pc.createOffer();
await pc.setLocalDescription(offer);
if (pc.canTrickleIceCandidates) return pc.localDescription;
const answer = await waitToCompleteIceGathering(pc);
sendAnswerToPeer(answer);
}
pc.addEventListener(
"icecandidate",
(e) => pc.canTrickleIceCandidates && sendCandidateToPeer(e.candidate),
);