Crude implementation of Writer for non-node environments

writer.ts

export class Writer extends EventTarget {
  writer: WritableStream;
  defaultWriter: WritableStreamDefaultWriter

  constructor(writer: WritableStream) {
    super();
    this.writer = writer;
    this.defaultWriter = writer.getWriter();
  }

  emit(event: string, data: any) {
    this.dispatchEvent(new Event(event));

    // TODO only on pipe
    if (event === 'pipe') {
      data.on('data', this.onData.bind(this));
      data.on('end', this.onEnd.bind(this));
    }
  }

  async onData(chunk: any) {
    await this.defaultWriter.ready;
    this.defaultWriter.write(chunk);
  }
  async onEnd() {
    this.emit('finish', null);
    await this.defaultWriter.ready;
    await this.defaultWriter.close();
  }
  end() { /* needed but writer.close must be called later. */ }
  on(evt: string, cb: EventListenerOrEventListenerObject) { this.addEventListener(evt, cb); return this; }
  removeListener(evt: string, cb: EventListenerOrEventListenerObject) { this.removeEventListener(evt, cb); }
}