webrtc P2P

RTCDataChannel

Signature

const channel = pc.createDataChannel(label, options);
// options: { ordered, maxRetransmits, maxPacketLifeTime, negotiated, id }

What it does

Carries arbitrary data (text, JSON, or binary) directly between peers over SCTP, without a server in the path. Delivery can be reliable and ordered or fast and lossy.

Key members

Member Kind Purpose
label property The channel name set at creation.
readyState property connecting, open, closing, closed.
ordered property Whether messages arrive in send order.
bufferedAmount property Bytes queued but not yet sent.
bufferedAmountLowThreshold property Threshold that fires bufferedamountlow.
binaryType property blob or arraybuffer for incoming binary.
send() method Send a string, ArrayBuffer, Blob, or typed array.
close() method Close the channel.
open / message / close / error event Lifecycle and inbound data.

Behaviour & constraints

  • Only call send() when readyState === 'open', or it throws.
  • maxRetransmits and maxPacketLifeTime are mutually exclusive; either makes the channel unreliable and implies unordered-friendly use.
  • Set negotiated: true with a fixed id to open both ends without the datachannel event.
  • Watch bufferedAmount to apply backpressure on large transfers; don't flood the buffer.
  • The non-creating peer receives the channel via the connection's datachannel event.

Example

const channel = pc.createDataChannel('chat');

channel.onopen = () => channel.send('hello');
channel.onmessage = (e) => console.log('peer said', e.data);

// remote side
pc.ondatachannel = ({ channel }) => {
  channel.onmessage = (e) => console.log(e.data);
};

See also