后端分页，每页的数量在后端定死的情况下，进行后端导出所有数据。（递归解决接口和分页数据放到excel流）

//后端每页返回的数据拼接的数组

  eventsConcatResult = (events: any[]) => {
        let eventExcel:any[]=[]
        for (let j = 0; j < events.length; j++) {
          let array = [];
          array.push(events[j].camera['_id'])
          array.push(events[j].camera.alias)
          array.push((events[j].camera.parent && events[j].camera.parent['_id']) ? events[j].camera.parent['_id'] : "无")
          array.push((events[j].camera.parent.parent && events[j].camera.parent.parent['_id']) ? events[j].camera.parent.parent['_id'] : "无")
          array.push(events[j].category)
          switch (events[j].category) {
            case 0:
              array.push("产品")
              break;
            case 1:
              array.push("报警")
              break;
            case -1:
              array.push("未知")
              break;
            default:
              break;
          }
          array.push(events[j].code)
          switch (events[j].code) {
            case 1:
              array.push("人进入")
              break;
            case 2:
              array.push("人离开")
              break;
            case 3:
              array.push("人停留")
              break;
            case -1:
              array.push("未知")
              break;
            default:
              break;
          }
          array.push(`${this.utilsService.$server}${events[j].video_url}`)
          array.push(events[j].event_timeStamp)
          array.push(events[j].timeStamp)
          eventExcel.push(array)
        }
    return eventExcel;
  };

//采用递归的方法实现循环内异步调用接口，并且循环一页将这页拼接的数组放到excel流里。

  excel(condition: EventSearchCondition) {
    this.wb= XLSX.utils.book_new();
    this.ws = XLSX.utils.aoa_to_sheet(this.excelData);
    this.utilsService.$http.post<any>(this.utilsService.$server + '/api/events', {
      condition: condition,
      sort: this.sort.active || null,
      order: this.sort.direction || null,
      pageNumber: 0,
      entriesPerPage: this.entriesPerPage
    }).subscribe(async (events: any) => {
      let pagesTotalCount = Math.ceil(events.totalEvents / this.entriesPerPage)-1
      const fetchSinglePage = (pageNumber: number): void => {
        if (pageNumber>pagesTotalCount){
          console.log(this.ws)
          XLSX.utils.book_append_sheet(this.wb, this.ws, 'event');
          XLSX.writeFile(this.wb, '事件记录.xlsx');
          return;
        }
        this.utilsService.$http.post<any>(this.utilsService.$server + '/api/events', {
          condition: condition,
          sort: this.sort.active || null,
          order: this.sort.direction || null,
          pageNumber:pageNumber,
          entriesPerPage: this.entriesPerPage
        }).subscribe((item: any) => {
          XLSX.utils.sheet_add_aoa(this.ws, this.eventsConcatResult(item.eventsList),{origin: -1});
          // console.log(this.ws)
          fetchSinglePage(pageNumber + 1)
        })
      }
      fetchSinglePage(0)
    })

  }

//调用接口

  async ExportExcel(){
    //获取原生的所有events
    await this.excel(this.searchCondition)
  }

//前端按钮

<button mat-button color="primary" (click)="ExportExcel()">{{ 'Export' | translate }}</button>