This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

The read-only RTCDataChannel property bufferedAmount returns the number of bytes of data currently queued to be sent over the data channel. The queue may build up as a result of calls to the send() method. This only includes data buffered by the user agent itself; it doesn't include any framing overhead or buffering done by the operating system or network hardware.

The user agent may implement the process of actually sending data in any way it chooses; this may be done periodically during the event loop or truly asynchronously. As messages are actually sent, this value is reduced accordingly.

Closing the data channel doesn't reset this count, even though the user agent purges the queued messages. However, even after closing the channel, attempts to send messages continue to add to the bufferedAmount value, even though the messages are neither sent nor buffered.

Whenever this value decreases to fall to or below the value specified in the bufferedAmountLowThreshold property, the user agent fires the bufferedamountlow event. This event may be used, for example, to implement code which queues more messages to be sent whenever there's room to buffer them.


var amount = aDataChannel.bufferedAmount;


The number of bytes of data currently queued to be sent over the data channel but have not yet been sent.


The snippet below includes a function which changes the contents of a block with the ID "bufferSize" to a string indicating the number of bytes currently buffered on an RTCDataChannel.

var dc = peerConnection.createDataChannel("File Transfer");
/* ... */

function showBufferedAmount(channel) {
  let el = document.getElementbyId("bufferSize");

  el.innerHTML = channel.bufferedAmount + " bytes";


Specification Status Comment
WebRTC 1.0: Real-time Communication Between Browser
The definition of 'RTCDataChannel.bufferedAmount' in that specification.
Working Draft Initial specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) 22 (22) [1] No support (Yes) ?
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support ? ? 22.0 (22) [1] No support ? ?

[1] The interface is called DataChannel and not RTCDataChannel in Firefox; however, a binding was added in Firefox 24 so that either name may be used.

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

bufferedAmount Experimental Property Read-only Reference RTCDataChannel WebRTC