files/en-us/web/api/compressionstream/writable/index.md
{{APIRef("Compression Streams API")}}{{AvailableInWorkers}}
The writable read-only property of the {{domxref("CompressionStream")}} interface returns a {{domxref("WritableStream")}} that accepts uncompressed data to be compressed, in the form of {{jsxref("ArrayBuffer")}}, {{jsxref("TypedArray")}}, or {{jsxref("DataView")}} chunks.
A {{domxref("WritableStream")}}.
This example creates a CompressionStream that performs gzip compression. It writes some binary data to the writable stream, then reads the compressed data from the readable stream.
const stream = new CompressionStream("gzip");
// Write data to be compressed
const data = new TextEncoder().encode("Hello, world!");
const writer = stream.writable.getWriter();
writer.write(data);
writer.close();
// Read compressed data
const reader = stream.readable.getReader();
let done = false;
let output = [];
while (!done) {
const result = await reader.read();
if (result.value) {
output.push(...result.value);
}
done = result.done;
}
console.log(new Uint8Array(output).toBase64()); // H4sIAAAAAAAAE/NIzcnJ11Eozy/KSVEEAObG5usNAAAA
{{Specifications}}
{{Compat}}