Web/API/WritableStreamDefaultWriter/ready

This is an experimental technologyCheck 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
StreamsThe definition of 'ready' in that specification.	Living Standard	Initial definition.

Browser Compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`ready` Experimental'	Chrome Full support 59	Edge Full support 16	Firefox No support No	IE No support No	Opera Full support 46	Safari ?	WebView Android Full support 59	Chrome Android Full support 59	Firefox Android No support No	Opera Android Full support 43	Safari 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.

WritableStreamDefaultWriter.ready by Mozilla Contributors is licensed under CC-BY-SA 2.5.