The RTCIceCandidate interface's read-only priority property specifies the candidate's priority according to the remote peer; the higher this value is, the better the remote peer considers the candidate to be.

The priority field's value is set from the candidateInfo options object passed to the RTCIceCandidate() constructor. You can't specify the value of priority directly in the options object, but its value is automatically extracted from the object's candidate a-line, if it's formatted properly.

A long, unsigned integer value indicating the priority of the candidate according to the remote peer. The larger this value is, the more preferable the remote peer considers this candidate to be.

priority is initialized to null if it is not specified in the candidate, or if the candidate string can't be parsed properly.

Consider this SDP attribute line (a-line) which describes an ICE candidate:

a=candidate:4234997325 1 udp 2043278322 192.0.2.172 44323 typ host

The priority is the number after the protocol, so it's the fourth field in the candidate string. In this example, the priority is 2043278322.

This candidate examines the priority of the candidate and, if it's greater than the priority of a previously-seen candidate, remembers the candidate for later use.

let bestCandidate = {
  candidate: "",
  sdpMid: null,
  sdpMLineIndex: null,
  priority: 0,
};

function handleCandidate(candidateString) {
  const candidate = new RTCIceCandidate(candidateString);

  if (candidate.priority > bestCandidate.priority) {
    bestCandidate = candidate;
  }
}