尽管收到有效数据，Promise 仍返回未定义

Question

'use strict';

let mongodb = require('mongodb')
let mongoose = require('mongoose')
const fetch = require("node-fetch");

module.exports = function (app) {

  mongoose.connect(process.env.DB, { useNewUrlParser: true, useUnifiedTopology: true })

  let stockSchema = new mongoose.Schema({
    name: { type: String, required: true},
    likes: { type: Number, default: 0},
    ips: [String]
  })

  let Stock = mongoose.model('Stock', stockSchema)
  
  app.route('/api/stock-prices')
    .get(function (req, res){

      let responseObject = {}
      
      let getPrice = (stock) => {
        let api = `https://stock-price-checker-proxy.freecodecamp.rocks/v1/stock/${stock}/quote`
        return fetch(api)
          .then(response => response.json())
          .then(data => {
            return data['latestPrice']
          })
      }
      
      let findStock = (stock) => {
        return Stock.findOne({name: stock}, (err, stockDoc) => {
          if (!err && stockDoc){
            return stockDoc
          }
        })
      }

      let findStockAndUpdate = (stock, update) => {
        return Stock.findOneAndUpdate({name: stock}, update, {new: true, upsert: true}, (err, updatedStock) => {
          if (!err && updatedStock){
            return updatedStock
          }
        })
      }

      let assign = (stockData, total_stock_num) => {
        if (total_stock_num === 1){
          responseObject['stockData'] = stockData
        } else {
          if (!responseObject['stockData']){
            responseObject['stockData'] = []
          }
          responseObject['stockData'].push(stockData)
        }
        return responseObject
      }

      let buildResponse = (stock_name, total_stock_num, like_bool) => {
        return findStock(stock_name).then(stockDoc => {
          let stockData = {}
          // if stock was liked
          if (like_bool){
            // if stock is found in DB and IP hasn't already liked stock
            if (!stockDoc || !stockDoc['ips'].includes(req.ip)){
              let update = { $inc: {likes: 1}, $push: {ips: req.ip} }
              findStockAndUpdate(stock_name, update).then(updatedStock => {
                getPrice(stock_name).then(price => {
                  stockData['stock'] = updatedStock['name']
                  stockData['price'] = price
                  stockData['likes'] = updatedStock['likes']
                  return assign(stockData, total_stock_num)
                })
              })
            }
          }
          // if stock wasn't liked, or IP has already liked stock
          if (!like_bool || (stockDoc && stockDoc['ips'].includes(req.ip))){
            getPrice(stock_name).then(price => {
              stockData['stock'] = stock_name
              stockData['price'] = price
              stockData['likes'] = stockDoc ? stockDoc['likes'] : 0
              return assign(stockData, total_stock_num)
            })
          }
        })
      }
      
      // if string, then only one stock was submitted
      if (typeof (req.query.stock) === 'string'){
        buildResponse(req.query.stock, 1, req.query.like).then(data => {
          console.log(data) // returns undefined
        })
      // if array, both stocks were submitted
      } else if (Array.isArray(req.query.stock)){
        let stockArr = req.query.stock

        buildResponse(stockArr[0], 2, req.query.like)
        buildResponse(stockArr[1], 2, req.query.like)
      }
    });
    
};

大家好，

谁能向我解释为什么我的 console.log 返回“未定义”而不是从 buildResponse() 函数接收到的对象？如果我从 buildResponse() 函数中将“assign(stockData, total_stock_num)”记录到控制台，则响应对象看起来不错，但是当我从 buildResponse() 返回它以在主要部分访问它时，它似乎丢失了我的代码。