RTCPeerConnection: createDataChannel() method
The createDataChannel()
method
on the RTCPeerConnection
interface
creates a new channel linked with the remote peer,
over which any kind of data may be transmitted.
This can be useful for back-channel content,
such as images, file transfer, text chat, game update
packets, and so forth.
If the new data channel is the first one added to the connection, renegotiation is
started by delivering a negotiationneeded
event.
Syntax
js
createDataChannel(label)
createDataChannel(label, options)
Parameters
label
-
A human-readable name for the channel. This string may not be longer than 65,535 bytes.
options
Optional-
An object providing configuration options for the data channel. It can contain the following fields:
ordered
Optional-
Indicates whether or not messages sent on the
RTCDataChannel
are required to arrive at their destination in the same order in which they were sent (true
), or if they're allowed to arrive out-of-order (false
). Default:true
. maxPacketLifeTime
Optional-
The maximum number of milliseconds that attempts to transfer a message may take in unreliable mode. While this value is a 16-bit unsigned number, each user agent may clamp it to whatever maximum it deems appropriate. Default:
null
. maxRetransmits
Optional-
The maximum number of times the user agent should attempt to retransmit a message which fails the first time in unreliable mode. While this value is a 16-bit unsigned number, each user agent may clamp it to whatever maximum it deems appropriate. Default:
null
. protocol
Optional-
The name of the sub-protocol being used on the
RTCDataChannel
, if any; otherwise, the empty string (""
). Default: empty string (""
). This string may not be longer than 65,535 bytes. negotiated
Optional-
By default (
false
), data channels are negotiated in-band, where one side callscreateDataChannel
, and the other side listens to theRTCDataChannelEvent
event using theondatachannel
event handler. Alternatively (true
), they can be negotiated out of-band, where both sides callcreateDataChannel
with an agreed-upon ID. Default:false
. id
Optional-
A 16-bit numeric ID for the channel; permitted values are 0 to 65534. If you don't include this option, the user agent will select an ID for you.
Note: These options represent the script-settable subset of the properties on the
RTCDataChannel
interface.
Return value
A new RTCDataChannel
object with the specified label
,
configured using the options specified by options
if that parameter is
included; otherwise, the defaults listed above are established.
Exceptions
InvalidStateError
DOMException
-
Thrown if the
RTCPeerConnection
is closed. TypeError
-
Thrown in the following situations:
- The label and/or protocol string is too long; these cannot be longer than 65,535 bytes (bytes, rather than characters).
-
The
id
is 65535. While this is a valid unsigned 16-bit value, it's not a permitted value forid
.
SyntaxError
DOMException
-
Thrown if values were specified for both the
maxPacketLifeTime
andmaxRetransmits
options. You may specify a non-null
value for only one of these. ResourceInUse
DOMException
-
Thrown if an
id
was specified, but anotherRTCDataChannel
is already using the same value. OperationError
DOMException
-
Thrown if either the specified
id
is already in use, or if noid
was specified, the WebRTC layer was unable to automatically generate an ID because all IDs are in use.
Examples
This example shows how to create a data channel and set up handlers for the
open
and message
events to send and receive messages on it
(For brevity, the example assumes onnegotiationneeded is set up).
js
// Offerer side
const pc = new RTCPeerConnection(options);
const channel = pc.createDataChannel("chat");
channel.onopen = (event) => {
channel.send("Hi you!");
};
channel.onmessage = (event) => {
console.log(event.data);
};
js
// Answerer side
const pc = new RTCPeerConnection(options);
pc.ondatachannel = (event) => {
const channel = event.channel;
channel.onopen = (event) => {
channel.send("Hi back!");
};
channel.onmessage = (event) => {
console.log(event.data);
};
};
Alternatively, more symmetrical out-of-band negotiation can be used, using an agreed-upon id (0 here):
js
// Both sides
const pc = new RTCPeerConnection(options);
const channel = pc.createDataChannel("chat", { negotiated: true, id: 0 });
channel.onopen = (event) => {
channel.send("Hi!");
};
channel.onmessage = (event) => {
console.log(event.data);
};
For a more thorough example showing how the connection and channel are established, see A simple RTCDataChannel sample.
Specifications
Specification |
---|
WebRTC: Real-Time Communication in Browsers # dom-peerconnection-createdatachannel |
Browser compatibility
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