WritableStreamDefaultWriter.ready

This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The ready read-only property of the WritableStreamDefaultWriter interface returns a Promise that resolves when the desired size of the stream's internal queue transitions from non-positive to positive, signaling that it is no longer applying backpressure.

Syntax

var promise = writableStreamDefaultWriter.ready;

Value

A Promise.

Example

The following example shows two uses of the ready property. The first uses ready to ensure that the WritableStream is done writing and thus able to receive data before sending a binary chunk. The second also checks whether the the WritableStream is done writing, but this time because the writing must be finished before the writer can be closed.

function sendMessage(message, writableStream) {
  // defaultWriter is of type WritableStreamDefaultWriter
  var defaultWriter = writableStream.getWriter();
  var encoder = new TextEncoder();
  var encoded = encoder.encode(message, {stream: true});
  encoded.forEach(function(chunk) {
    // Make sure the stream and its writer are able to
    //   receive data.
    defaultWriter.ready
    .then(function() {
      defaultWriter.write(chunk)
      .then(function() {
        console.log("Chunk written to sink.);
      })
      .catch(function(err) {
        console.log("Chunk error: " + err);
      });
    });
    // Call ready again to ensure that all chunks are written
    //   before closing the writer.
    defaultWriter.ready
    .then(function() {
      defaultWriter.close()
      .then(function() {
        console.log("All chunks written");
      })
      .catch(function(err) {
        console.log("Stream error: " + err);
      });
    });
  });
}

Specifications

Specification Status Comment
Streams
The definition of 'ready' in that specification.
Living Standard Initial definition.

Browser Compatibility

DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
ready
Experimental
Chrome Full support 59Edge Full support 16Firefox No support NoIE No support NoOpera Full support 46Safari ? WebView Android Full support 59Chrome Android Full support 59Firefox Android No support NoOpera Android Full support 43Safari iOS ? Samsung Internet Android Full support 7.0

Legend

Full support
Full support
No support
No support
Compatibility unknown
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.