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In this article we will see how to create a QR code in ExpressJS.

We install the required NPM package.


npm install qrcode --save

This module can create PNG files both as data URLs and as actual files. So let's define a utility function for file management.


'use strict';

const fs = require('fs');
const util = require('util');

const exists = util.promisify(fs.access);

module.exports = {
    fileExists(path) {
        return new Promise((resolve, reject) => {
            exists(path, fs.F_OK).then(ok => {
                resolve(true);
            }).catch(err => {
               resolve(false);
            });
        });
    }
};

We then define a route with conditional logic: if the GET request is made with AJAX, a data URL is generated, otherwise it is served the PNG file created.


'use strict';

const fs = require('fs');
const path = require('path');
const express = require('express');
const QRCode = require('qrcode');
const utils = require('./utils');
const app = express();
const port = process.env.PORT || 3000;

app.disable('x-powered-by');
app.use('/public', express.static(path.join(__dirname, 'public')));

app.get('/qrcode', async (req, res) => {
    try {

        const qrCodeText = 'https://site.tld';

        if(req.xhr) {
            const url = await QRCode.toDataURL(qrCodeText);
            res.json({url});
        } else {
           const src = './public/images/qrcode.png';
           const exists = await utils.fileExists(src);
           if(!exists) {
               const stream = fs.createWriteStream(src);
               const code = await QRCode.toFileStream(stream, qrCodeText);
           }
           res.sendFile(src);
        }
    } catch(err) {
        res.json(err);
    }
});

app.listen(port);

A typical use of the AJAX mode is when the QR code is displayed asynchronously as in the following example.


"use strict";

$(function() {
    $.get( "/qrcode", function( response ) {
        $( "#qrcode-image" ).attr( "src", response.url ).show();
    });
});

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