Node router for marketplace routes

Question

After cleaning up & some refactoring, one module of my code became like below. However, I'm feeling like there's still some unnecessary redundancy, and it can be improved further and look neater.

But I can't come up with exactly how to do it.

'use strict';

// === showing the execution context ==============

const express = require('express');
const router = express.Router();

const moment = require("moment");
const momentDurationSetup = require("moment-duration-format");
const DB = require('./DBOperator');
const _ = require('lodash');

const Promise = require("bluebird");
const request = require('superagent-bluebird-promise');

const utils = require('../utils');


// ========== main concern area ===============

function realTime(queryFunction, payload, req, res, next) {
    queryFunction((err, results) => {
        if (err) {
            console.log(err);
            next();
        } else {
            res.json({data: _.get(results[0].rows[0], payload, -1)});
        }
    });
}

router.get('/online-buyer-count', utils.mcache(15), (req, res, next) => {
    realTime(DB.onlinebuyerNumQuery, 'onlinebuyerNum', req, res, next);
});

router.get('/offline-buyer-count', utils.mcache(15), (req, res, next) => {
    realTime(DB.offlinebuyerNumQuery, 'offlinebuyerNum', req, res, next);
});

router.get('/online-seller-count', utils.mcache(15), (req, res, next) => {
    realTime(DB.onlinesellerNumQuery, 'onlinesellerNum', req, res, next);
});

router.get('/offline-seller-count', utils.mcache(15), (req, res, next) => {
    realTime(DB.offlinesellerNumQuery, 'offlinesellerNum', req, res, next);
});


/ ===========================

module.exports = router;

Answer 1

Partial application

One way to simplify the code is to eliminate the lambda/anonymous functions using Function.bind() to create Partially applied functions. For instance:

router.get('/online-buyer-count', utils.mcache(15), (req, res, next) => {
    realTime(DB.onlinebuyerNumQuery, 'onlinebuyerNum', req, res, next);
});

can be simplified to

router.get('/online-buyer-count', realTime.bind(null, DB.onlinebuyerNumQuery, 'onlinebuyerNum'));

And similarly for the other three routes, which reduces 12 lines to 4.

looping over the routes

The redundancy could also be simplified using Array.forEach()

['online', 'offline'].forEach(mode => { 
    ['buyer', 'seller'].forEach(role => {
        router.get('/'+mode+'-'+role+'-count', realTime.bind(null, DB[mode+role+'NumQuery'], mode+role+'Num'));
    });
});

Taking that one step further using more partially-applied functions, the callback function of the inner forEach can be pulled out to a separate function:

const addRoute = (mode, role) => router.get('/'+mode+'-'+role+'-count', realTime.bind(null, DB[mode+role+'NumQuery'], mode+role+'Num'));

And then that function can be made into a partial and used within the nested forEach:

['online', 'offline'].forEach(mode => ['buyer', 'seller'].forEach(addRoute.bind(null, mode)));

So that can reduce those 4 lines to 2. It may be desirable to break those up into multiple lines for readability.