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The number of bytes of data that have been queued using calls to send() but not yet transmitted to the network.

Property of apis/websocket/WebSocketapis/websocket/WebSocket


Note: This property is read-only.

var result = element.bufferedAmount;

Return Value

Returns an object of type unsigned longunsigned long


var data = new ArrayBuffer(10000000);

// perform some operations on the ArrayBuffer

if (socket.bufferedAmount === 0) {
  // the data sent
else {
  // the data did not send


This can be used to determine whether the network can handle the data rate you are sending. The value does not reset to zero when the connection is closed; if you keep calling send(), this will continue to climb.

Related specifications

W3C WebSocket Specification
W3C Candidate Recommendation