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Data channels

The WebRTC standard also covers an API for sending arbitrary data over a RTCPeerConnection. This is done by calling createDataChannel() on a RTCPeerConnection object, which returns a RTCDataChannel object.

const peerConnection = new RTCPeerConnection(configuration);
const dataChannel = peerConnection.createDataChannel();

The remote peer can receive data channels by listening for the datachannel event on the RTCPeerConnection object. The received event is of the type RTCDataChannelEvent and contains a channel property that represents the RTCDataChannel connected between the peers.

const peerConnection = new RTCPeerConnection(configuration);
peerConnection.addEventListener('datachannel', event => {
    const dataChannel = event.channel;
});

Open and close events

Before a data channel can be used for sending data, the client needs to wait until it has been opened. This is done by listening to the open event. Likewise, there is a close event for when either side closes the channel.

const messageBox = document.querySelector('#messageBox');
const sendButton = document.querySelector('#sendButton');
const peerConnection = new RTCPeerConnection(configuration);
const dataChannel = peerConnection.createDataChannel();

// Enable textarea and button when opened
dataChannel.addEventListener('open', event => {
    messageBox.disabled = false;
    messageBox.focus();
    sendButton.disabled = false;
});

// Disable input when closed
dataChannel.addEventListener('close', event => {
    messageBox.disabled = false;
    sendButton.disabled = false;
});

Messages

Sending a message on a RTCDataChannel is done by calling the send() function with the data we want to send. The data parameter for this function can be either a string, a Blob, an ArrayBuffer or and ArrayBufferView.

const messageBox = document.querySelector('#messageBox');
const sendButton = document.querySelector('#sendButton');

// Send a simple text message when we click the button
sendButton.addEventListener('click', event => {
    const message = messageBox.textContent;
    dataChannel.send(message);
})

The remote peer will receive messages sent on a RTCDataChannel by listening on the message event.

const incomingMessages = document.querySelector('#incomingMessages');

const peerConnection = new RTCPeerConnection(configuration);
const dataChannel = peerConnection.createDataChannel();

// Append new messages to the box of incoming messages
dataChannel.addEventListener('message', event => {
    const message = event.data;
    incomingMessages.textContent += message + '\n';
});