Node.js Tips

Node.js Tips — Excel Files, Flash Messages, and Response Data

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Like any kind of apps, there are difficult issues to solve when we write Node apps.

In this article, we’ll look at some solutions to common problems when writing Node apps.

Correctly Exporting async Functions in Node.js

We can export an async function like any other function.

For instance, we can write:

async function doSomething() {
  // ...

module.exports.doSomething = doSomething;

We export doSomething like we can with any other function.

ReadFile in Base64 Nodejs

We can read a file into a base64 string by using the readFileSync method.

For instance, we can write:

const fs = require('fs');
const str = fs.readFileSync('/path/to/file.jpg', { encoding: 'base64' });

We pass in the 2nd argument with an object.

It has the encoding property set to 'base64' so that we can parse the file into a base64 string.

It’s returned and assigned to str .

Find and Update Subdocument with Mongoose

We can find and update a subdocument with the findOneAndUpdate method.

For instance, we can write:

  { "_id": personId, "address._id": address._id },
    "$set": {
      "address.$": address
  (err, doc) => {

We call the findOneAndUpdate method with a few arguments.

The first is the query to find the object to update.

We query both the parent document and the subdocument with it.

We query the person document by ID, and address with the address._id .

The 2nd argument is the $set method to set the value for the address.$ to set the address subdocument.

The $ is the positional operator variable.

It’s used to get the subdocument that matches the given position.

Then the callback has the results once the operation is done.

Skip Subsequent Mocha Tests from Spec if One Fails

Mocha has a bail operation to skip the remaining tests if one fails.

We can also use b for short.

Returning data from Axios API

To get data from an HTTP request made by Axios, we can return the object in our then callback.

For instance, we can write:

  .then(response => {
  then(data => {

We call res.json with the response data after the request is made successfully.

Read the Body of a Fetch Promise

We can get the body of a Fetch promise by using the json method to convert the response object to a JSON object.

For instance, we can write:

  .then(response => response.json())
  .then‌​(data => console.log(data))

We called response.json() to get the JSON.

Parse XLSX with Node and Create JSON

To make parsing XLSX files easy in a Node app, we can use the xlsx package.

We can use it by writing:

const XLSX = require('xlsx');
const workbook = XLSX.readFile('spreadsheet.xlsx');
const [sheetName] = workbook.SheetNames;
const json = XLSX.utils.sheet_to_json(workbook.Sheets[sheetName])

We use the xlsx package.

Then we can use the readFile to read the spreadsheet with the given path.

The workbook.SheetNames property get the sheet names from the XLSX file.

We get the first name with our example.

Then we call sheet_to_json to convert the sheet with the given name.

We get the sheet by using the workbook.Sheets object.

Check if a JSON is Empty in NodeJS

We can check if a JSON object is empty with the Object.keys method.

For example, we can write:

Object.keys(obj).length === 0;

where obj is the JSON object we want to check.

Send Flash Messages in Express

A flash message is a message that’s stored during a session.

We can use the connect-flash middleware to send a flash message to the template.

To install the package, we run:

npm install connect-flash

Then we can write:

const flash = require('connect-flash');
const app = express();

app.configure(function() {
  app.use(express.session({ cookie: { maxAge: 60000 }}));

app.get('/flash', (req, res) => {
  req.flash('info', 'flash message');

app.get('/', (req, res) => {
  res.render('index', { messages: req.flash('info') });

We set the flash message with req.flash .

The first argument is the key of the message.

The 2nd argument is the message itself.

We can get the message by the key if we use req.flash with one argument as we did on the '/' route.


We can export async functions like any other function.

The connect-flash package lets us store messages that are available during the session.

The xlsx package lets us parse data from XLSX files.

Subdocuments can be updated with Mongoose.

We can get the response data with various HTTP clients.

By John Au-Yeung

Web developer specializing in React, Vue, and front end development.

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