Streams — ReadableStream / WritableStream / CompressionStream / DecompressionStream

Web Streams API with async iteration, piping, and teeing.

ReadableStream

Create

// From underlying source
const stream = new ReadableStream({
  start(controller) {
    controller.enqueue(new Uint8Array([1, 2, 3]));
    controller.close();
  },
});

// From fetch response
const response = await fetch(url);
const reader = response.body.getReader();

Read

// Reader mode
const reader = stream.getReader();
while (true) {
  const { value, done } = await reader.read();
  if (done) break;
  console.log(value); // Uint8Array chunk
}

// Async iteration (recommended)
for await (const chunk of stream) {
  console.log(chunk);
}

Pipe

await readable.pipeTo(writable);

// With options
await readable.pipeTo(writable, {
  preventClose: false,
  preventAbort: false,
  preventCancel: false,
  signal: controller.signal,
});

const transformed = readable.pipeThrough(new CompressionStream("gzip"));

Tee

const [branch1, branch2] = stream.tee();

Properties & Methods

Method / Property	Description
locked	Whether locked by a reader
getReader()	Acquire reader (locks the stream)
cancel(reason?)	Cancel the stream
pipeTo(dest, options?)	Pipe to WritableStream
pipeThrough(transform, options?)	Pipe through an object exposing readable and writable
tee()	Split into two streams
[Symbol.asyncIterator]	Supports for await...of

---

WritableStream

Create

const writable = new WritableStream({
  write(chunk) {
    console.log("received:", chunk);
  },
  close() {
    console.log("stream closed");
  },
  abort(reason) {
    console.log("aborted:", reason);
  },
});

Write

const writer = writable.getWriter();
await writer.write(new Uint8Array([1, 2, 3]));
await writer.write(new Uint8Array([4, 5, 6]));
await writer.close();

Properties & Methods

Method / Property	Description
locked	Whether locked by a writer
getWriter()	Acquire writer (locks the stream)
abort(reason?)	Abort the stream

Writer Methods

Method	Description
write(chunk)	Write a chunk
close()	Close the stream
abort(reason?)	Abort the stream
releaseLock()	Release the lock

---

Common Patterns

Download and process

const response = await fetch("https://example.com/large-file");
for await (const chunk of response.body) {
  process(chunk);
}

Pipe to file

const response = await fetch(sourceUrl);
const writable = file.writer();
await response.body.pipeTo(writable);

---

CompressionStream

Supported formats:

• "gzip"
• "deflate"
• "deflate-raw"

const compressed = source.pipeThrough(new CompressionStream("gzip"));

Properties

Method / Property	Description
readable	Compressed output ReadableStream
writable	Input WritableStream

---

DecompressionStream

Supported formats:

• "gzip"
• "deflate"
• "deflate-raw"

const decompressed = source.pipeThrough(new DecompressionStream("gzip"));

Properties

Method / Property	Description
readable	Decompressed output ReadableStream
writable	Input WritableStream