infinity loop bug.ts

  /*use this function*/
  buy() {
    let UserId = 'test';
    this.Queue = this.list.buy(this.UserProduct);
    this.Queue.subscribe(data=> {
      console.log(data.length);
      if (data.length == 0 ){
          this.list.FirstOrder(UserId,this.UserProduct);
      }else if(data.length >= 1){
          console.log(data.length)
          this.list.NextOrder(data.length,UserId,this.UserProduct);
      }
    });

  }

/*function when lenght = 0*/
FirstOrder(UserId: string, ProductId: any[]) {
    let add = this.af.database.list(`Order`);
    let i = 1;
    for (let Id of ProductId) {
      add.push({
          Queue: i,
          UserId: UserId,
          ProductId: Id.ProductId,
          MerchantId: ProductId[0].MerchantId
        }
      );
      i += 1;
    }
  }

/*function when length != 0 */
 NextOrder(Queue: number, UserId: string, ProductId: any[]) {
    let add = this.af.database.list(`Order`);
    let i = Queue + 1;
    for (let Id of ProductId) {
      add.push({
          Queue: i,
          UserId: UserId,
          ProductId: Id.ProductId,
          MerchantId: ProductId[0].MerchantId
        }
      );
      i += 1;
    }
    ProductId = null;
  }
}