Method shift

src/main/pp-ocr.ts:17–22

()

    super();
  }
  shift() {
    this.length &&
      Promise.resolve(this[0]()).then(
        () => (super.shift(), this.status && this.shift())
      );
  }
  push(cb: any): number {
    super.push(cb) - 1 || (this.status && this.shift());
    return 0;