RTCPeerConnection.createDataChannel()

语法

createDataChannel(label)
createDataChannel(label, options)

参数

label

一个便于理解的通道名。该字符串不能长于 65,535 字节.

options 可选

提供 data channel 设置的一个 RTCDataChannelInit dictionary

RTCDataChannelInit dictionary

RTCDataChannelInit 字典提供以下字段，用以构造可选的 options 参数来设置 data channel 以满足你的需求：

ordered 可选

表示通过 RTCDataChannel 的信息的到达顺序需要和发送顺序一致 (true), 或者到达顺序不需要和发送顺序一致 (false). 默认：true.

maxPacketLifeTime 可选

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 可选

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 a16-bit unsigned number, each user agent may clamp it to whatever maximum it deems appropriate. Default: null.

protocol 可选

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 可选

By default (false), data channels are negotiated in-band, where one side calls createDataChannel, and the other side listens to the RTCDataChannelEvent event using the ondatachannel EventHandler . Alternatively (true), they can be negotiated out of-band, where both sides call createDataChannel with an agreed-upon id. Default: false.

id 可选

An 16-bit numeric ID for the channel; permitted values are 0-65534. If you don't include this option, the user agent will select an ID for you.

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

The RTCPeerConnection is closed.

TypeError

This can happen in a couple of 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 for id.

SyntaxError

Values were specified for both the maxPacketLifeTime and maxRetransmits options. You may only specify a non-null value for one of these.

ResourceInUse

An id was specified, but another RTCDataChannel is already using the same value.

OperationError

Either the specified id is already in use or, if no id 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 brievity, the example assumes onnegotiationneeded is set up).

// Offerer side

var pc = new RTCPeerConnection(options);
var channel = pc.createDataChannel("chat");
channel.onopen = function (event) {
  channel.send("Hi you!");
};
channel.onmessage = function (event) {
  console.log(event.data);
};

// Answerer side

var pc = new RTCPeerConnection(options);
pc.ondatachannel = function (event) {
  var channel = event.channel;
  channel.onopen = function (event) {
    channel.send("Hi back!");
  };
  channel.onmessage = function (event) {
    console.log(event.data);
  };
};

Alternatively, more symmetrical out-of-band negotiation can be used, using an agreed-upon id (0 here):

// Both sides

var pc = new RTCPeerConnection(options);
var channel = pc.createDataChannel("chat", { negotiated: true, id: 0 });
channel.onopen = function (event) {
  channel.send("Hi!");
};
channel.onmessage = function (event) {
  console.log(event.data);
};

For a more thorough example showing how the connection and channel are established, see A simple RTCDataChannel sample.

Specifications

Browser compatibility

See also

• RTCDataChannel
• A simple RTCDataChannel sample
• RTCPeerConnection