HTTP redirects with flash messages in ExpressJS

In ExpressJS we can implement flash messages in HTTP redirects using a specific NPM module.

connect-flash is a module that actually helps us to add a feature already present in frameworks such as Laravel, that is the HTTP redirect with a message to show in the views.

This module is based on the sessions that we can create and manage with the module express-session. To use it in Express, we then create a session and then include the module as middleware.

'use strict';

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

const app = express();

app.use(session({
  secret: 'secret key',
  resave: false,
  saveUninitialized: false
}));

app.use(flash());

This middleware adds the flash() method to the request object. Used as a setter, we can set up a message like this.

app.get('/logout', (req, res) => {
    req.flash('message', 'You are now logged out.');
    res.redirect('/');
});

The message consists of a key (in the example it is message) and a value. If you want you can add more values using an array.

req.flash('message', ['You are now logged out.', 'Login']);

So we can retrieve the message using the same method as getter passing the key as the only argument.

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

In the views we can show the message like this:

<% if (message) { %>
    <div class="alert alert-info"><%= message %></div>
<% } %>

In conclusion, this module proves extremely effective to implement a very useful feature when doing HTTP redirects we and don't want to use a query string.