WritableStreamDefaultWriter.ready

Experimental: 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 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
Streams Standard # ref-for-default-writer-ready⑨

Browser compatibility

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