server.js

const express = require('express');
const bodyParser = require('body-parser')
const path = require('path');
const multer = require('multer');
const unlink = require('fs').unlink;

const convertor = require('./src/components/xlsx-convertor');

const app = express();

app.use('/', express.static(path.join(__dirname, 'build')));

var storage = multer.diskStorage({ //multers disk storage settings
    destination: (req, file, cb) => {
        cb(null, (path.join(__dirname, '/uploads')))
    },
    filename: (req, file, cb) => {
        var datetimestamp = Date.now();
        cb(null, `${file.fieldname}-${datetimestamp}.${file.originalname.split('.')[file.originalname.split('.').length - 1]}`);
    }
});
var upload = multer({ //multer settings
    storage: storage,
    fileFilter: (req, file, callback) => { //file filter
        if (['xls', 'xlsx'].indexOf(file.originalname.split('.')[file.originalname.split('.').length - 1]) === -1) {
            return callback(new Error('Wrong extension type'));
        }
        callback(null, true);
    }
}).single('file');
/** API path that will upload the files */
app.post('/upload', (req, res) => {
    upload(req, res, (err) => {
        if (err) {
            res.json({ error_code: 1, err_desc: err });
            return;
        }
        /** Multer gives us file info in req.file object */
        if (!req.file) {
            res.json({ error_code: 1, err_desc: "No file passed" });
            return;
        }
        /** Check the extension of the incoming file and 
         *  use the convertor
         */
        if (req.file.originalname.split('.')[req.file.originalname.split('.').length - 1] === 'xlsx') {
            try {
                convertor({
                    input: req.file.path,
                    output: null, //since we don't need output.json
                    lowerCaseHeaders: true
                }, (err, result) => {
                    if (err) {
                        return res.json({ error_code: 1, err_desc: err, data: null });
                    }
                    res.json({data: result });
                    unlink(req.file.path, (err) => {
                        if (err) throw err;
                      });
                });
            } catch (e) {
                console.log(e);
                res.json({ error_code: 1, err_desc: "Corupted excel file" });
            }
        }        
    })
});

app.get('/', function (req, res) {
  res.sendFile(path.join(__dirname, 'build', 'index.html'));
});

const port = process.env.PORT || 8080

app.listen(port, () => {
    console.log(`Express Runnning on ${port}`);
});