WritableStreamDefaultWriter: desiredSize property

The desiredSize read-only property of the WritableStreamDefaultWriter interface returns the desired size required to fill the stream's internal queue.

Value

An integer. Note that this can be negative if the queue is over-full.

The value will be null if the stream cannot be successfully written to (due to either being errored, or having an abort queued up), and zero if the stream is closed.

Exceptions

TypeError: The writer's lock is released.

Examples

const writableStream = new WritableStream(
  {
    write(chunk) {
      // ...
    },
    close() {
      // ...
    },
    abort(err) {
      // ...
    },
  },
  queuingStrategy
);

// ...

const writer = writableStream.getWriter();

// ...

// return stream's desired size
let size = writer.desiredSize;

Specifications

Specification
Streams Standard # ref-for-default-writer-desired-size⑥

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