--- title: RTCPeerConnection.createDataChannel() slug: Web/API/RTCPeerConnection/createDataChannel translation_of: Web/API/RTCPeerConnection/createDataChannel ---

{{APIRef("WebRTC")}}{{SeeCompatTable}}

{{domxref("RTCPeerConnection")}} 的 createDataChannel() 方法创建一个可以发送任意数据的数据通道(data channel)。常用于后台传输内容, 例如: 图像, 文件传输, 聊天文字, 游戏数据更新包, 等等。

基于某个连接创建第一个data channel时, 会通过发送一个{{event("negotiationneeded")}} event来开始重新谈判(renegotiation)。

语法

dataChannel = RTCPeerConnection.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 {{optional_inline}}
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 {{optional_inline}}
表示通过 {{domxref("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 {{optional_inline}}
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_inline}}
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 {{optional_inline}}
The name of the sub-protocol being used on the {{domxref("RTCDataChannel")}}, if any; otherwise, the empty string (""). Default: empty string, "". This string may not be longer than 65,535 bytes.
negotiated {{optional_inline}}
By default (false), data channels are negotiated in-band, where one side calls createDataChannel, and the other side listens to the {{domxref("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 {{optional_inline}}
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.

The options which can be configured using the RTCDataChannelInit dictionary represent the script-settable subset of the properties on the {{domxref("RTCDataChannel")}} interface.

Return value

A new {{domxref("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 {{domxref("RTCPeerConnection")}} is closed.
TypeError
This can happen in a couple of situations:
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 {{domxref("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 {{event("open")}} and {{event("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

Specification Status Comment
{{SpecName('WebRTC 1.0', '#widl-RTCPeerConnection-createDataChannel-RTCDataChannel-DOMString-label-RTCDataChannelInit-dataChannelDict', 'createDataChannel()')}} {{Spec2('WebRTC 1.0')}} Initial definition.

Browser compatibility

{{Compat("api.RTCPeerConnection.createDataChannel")}}

See also