前端代码
通过a标签href属性去链接api

 <a download="文件名" href={`/api/monitor/customer_order/export`}>
                  下载生成execl
              </a>

egg代码

在extend文件夹下新建helper.js文件
app/extend/helper.js

const XLSX = require('xlsx');

module.exports = {
  exportXLSX(
    fileName = 'file',
    sheetName = 'sheet1',
    header,
    data,
  ) {
    // 生成workbook
    const workbook = XLSX.utils.book_new();
    // 插入表头
    const headerData = [header, ...data];
    // 生成worksheet
    const worksheet = XLSX.utils.json_to_sheet(headerData, { skipHeader: true });
    // 组装
    XLSX.utils.book_append_sheet(workbook, worksheet, sheetName);
  
    // 返回数据流
    // @ts-ignore
    this.ctx.set('Content-Type', 'application/vnd.openxmlformats');
    // @ts-ignore
    this.ctx.set(
      'Content-Disposition',
      "attachment;filename*=UTF-8' '" + encodeURIComponent(fileName) + '.xlsx',
    );
    // @ts-ignore
    this.ctx.body = XLSX.write(workbook, {
      bookType: 'xlsx',
      type: 'buffer',
    });
  }
}

controller文件夹下home.js

'use strict';

const Controller = require('egg').Controller;

class HomeController extends Controller {

  // 下载生成execl
  async toexecl() {
    const { ctx } = this;
    const query = ctx.queries;
    const result = await ctx.service.user.getUserList();
    if(result.length === 0) {
      ctx.success = {
        data: { ...result }
      }
      return;
    }
    const headerMap = {
      id: 'id',
      alarm_type: 'alarm_type',
      alarm_reason: 'alarm_reason',
      productline_id: 'productline_id',
      business_type: 'business_type',
      new_category: 'new_category',
      alarm_time: 'alarm_time',
      count: 'count',
      alarm_id: 'alarm_id',
      dm_subject: 'dm_subject',
      app_id: 'app_id'
    };
    await ctx.helper.exportXLSX('mbgtable', 'mbgtable', headerMap, result)
  }
}

module.exports = HomeController;

ctx.service.user.getUserList() 为链接数据库数据方案；