Method refill

tfjs-data/src/iterators/lazy_iterator.ts:1116–1121

* Refill the prefetch buffer. Returns only after the buffer is full, or * the upstream source is exhausted.

()

   * the upstream source is exhausted.
   */
  protected refill() {
    while (!this.buffer.isFull()) {
      const v = this.upstream.next();
      this.buffer.push(v);
    }
  }

  next(): Promise<IteratorResult<T>> {
    this.refill();