TransformStream

const transformContent = { start() {}, // required. async transform(chunk, controller) { chunk = await chunk; switch (typeof chunk) { case "object": // just say the stream is done I guess if (chunk === null) { controller.terminate(); } else if (ArrayBuffer.isView(chunk)) { controller.enqueue( new Uint8Array(chunk.buffer, chunk.byteOffset, chunk.byteLength), ); } else if ( Array.isArray(chunk) && chunk.every((value) => typeof value === "number") ) { controller.enqueue(new Uint8Array(chunk)); } else if ( typeof chunk.valueOf === "function" && chunk.valueOf() !== chunk ) { this.transform(chunk.valueOf(), controller); // hack } else if ("toJSON" in chunk) { this.transform(JSON.stringify(chunk), controller); } break; case "symbol": controller.error("Cannot send a symbol as a chunk part"); break; case "undefined": controller.error("Cannot send undefined as a chunk part"); break; default: controller.enqueue(this.textencoder.encode(String(chunk))); break; } }, flush() { /* do any destructor work here */ }, }; class AnyToU8Stream extends TransformStream { constructor() { super({ ...transformContent, textencoder: new TextEncoder() }); } }

let responses = [ /* conjoined response tree */ ]; let { readable, writable } = new TransformStream(); responses.reduce( (a, res, i, arr) => a.then(() => res.pipeTo(writable, { preventClose: i + 1 !== arr.length })), Promise.resolve(), );