小程序云函数多个函数的同步使用

以“获取文章评论列表”功能为例子，分以下几个步骤完成：
1、根据文章id获取评论列表（评论需要分页，所以还需page，limit参数）；
2、评论有上下级关系（回复评论），循环获取子评论；
3、获取评论的用户信息；
4、时间格式化（小程序云服务器提供的系统时间需要进行格式化，如不需要可）

// 云函数入口文件
const cloud = require('wx-server-sdk')
cloud.init()
// 云函数入口函数
exports.main = async(event, context) => {
  // 获取评论列表
  let {
    id,
    page,
    limit
  } = event;

  let base_data = [];

  const db = cloud.database()
  const db_comment = db.collection('comment');
  const db_user = db.collection('user');
  // 获取评论
  let comments = await (db_comment.where({
      article_id: id,
      comment_id: null
    }).orderBy('created_at', 'desc')
    .skip(limit * (page - 1))
    .limit(limit)
    .get());
  for (let i = 0; i < comments.data.length; i++) {
    // 获取子评论
    let comments_children = await (db_comment.where({
        article_id: id,
        comment_id: comments.data[i]._id
      }).orderBy('created_at', 'asc')
      .skip(0)
      .limit(9)
      .get());
    let _children = [];
    for (let i = 0; i < comments_children.data.length; i++) {
      // 获取用户
      let user = await (db_user.where({
        openid: comments_children.data[i].openid
      }).get())
      // 时间格式化
      let created_at = utc2beijing(comments_children.data[i].created_at, 'yyyy-MM-dd hh:mm');
      comments_children.data[i].created_at = created_at;
      let info = user.data[0].info;
      info['openId'] = user.data[0].openid;
      _children.push({
        comment: comments_children.data[i],
        user: info
      })
    }
    comments.data[i]['children'] = _children;
    // 获取用户
    let user = await (db_user.where({
      openid: comments.data[i].openid
    }).get())
    // 时间格式化
    let created_at = utc2beijing(comments.data[i].created_at, 'yyyy-MM-dd hh:mm');
    comments.data[i].created_at = created_at;
    base_data.push({
      comment: comments.data[i],
      user: user.data[0].info
    })
  }

  return base_data;

  /**
   * 时间转换
   */
  function utc2beijing(utc_datetime, format) {
    let timestamp = utc_datetime.getTime();
    // 增加8个小时，北京时间比utc时间多八个时区
    timestamp = timestamp + 8 * 60 * 60 * 1000;
    return dateFormat((parseInt(timestamp)), format);
  }

  function dateFormat(timestamp, format) {
    if (!format) {
      format = "yyyy-MM-dd hh:mm:ss";
    }
    timestamp = parseInt(timestamp);
    var realDate = new Date(timestamp);

    function timeFormat(num) {
      return num < 10 ? '0' + num : num;
    }
    var date = [
      ["M+", timeFormat(realDate.getMonth() + 1)],
      ["d+", timeFormat(realDate.getDate())],
      ["h+", timeFormat(realDate.getHours())],
      ["m+", timeFormat(realDate.getMinutes())],
      ["s+", timeFormat(realDate.getSeconds())],
      ["q+", Math.floor((realDate.getMonth() + 3) / 3)],
      ["S+", realDate.getMilliseconds()],
    ];
    var regYear = new RegExp("(y+)", "i");
    var reg1 = regYear.exec(format);

    if (reg1) {

      format = format.replace(reg1[1], (realDate.getFullYear() + '').substring(4 - reg1[1].length));
    }
    for (var i = 0; i < date.length; i++) {
      var k = date[i][0];
      var v = date[i][1];

      var reg2 = new RegExp("(" + k + ")").exec(format);
      if (reg2) {
        format = format.replace(reg2[1], reg2[1].length == 1 ?
          v : ("00" + v).substring(("" + v).length));
      }
    }
    return format;
  }

}