DEV Community

Jaime Rios
Jaime Rios

Posted on

Front End Development Automation. Part 4


In this post we will create part of a system that is part of a bigger one. We will focus only on running performance test.

Note: In this post I am assuming that you are quite familiar with Git, Github Webhooks, NodeJS and Docker.

NodeJS: Here is the repo with all the code.

The problem

ABC Corp has a SPA that is core to the business. It needs to perform great on mobile(we will define what great means later). As time goes by, releases become more frequent and there is a pressing need to ensure that all new releases comply with the performance budget assigned to it

The solution

As developers, we must ensure each release must be in a deployable state. For us, deployable means that all tests are passing and new features work as expected in an production-like environment. On top of that, we need/would like to have a way to get instant feedback about the performance of our next release, therefore the proposed solution:

Create a system that runs performance tests each time a new release is made.


  • dotenv. A zero-dependency module that loads environment variables from a .env file into process.env
  • NodeJS.
  • Puppeteer. Headless Chrome Node API.<!-- * ShellJS. Unix shell commands on top of the Node.js API -->
  • Lightouse CLI. Audit our application and get the relevant data.

1. Developing our Analysis tool

Ideally, our next build should always either improve upon the last release or stay within an acceptable range. If things start to deviate, we want to get the relevant data as fast as posible.

We will create a function that gathers these metrics:

  • JS Coverage & CSS Coverage. This metric tells us how much code was used, versus how much was loaded.
  • Network Requests. Lists the network requests that were made during page load.
  • Speed-index. Speed Index shows how quickly the contents of a page are visibly populated.

We will runs all tests that Lighthouse has available. This is the order in which things should start to happen:

  1. Get the app URL running in a testing/staging/local environment. This should be read from a configuration file.
  2. Generate code coverage. For now we'll just get it for the home page.
  3. Run Lighthouse audit.
  4. Filter information and send it somewhere it can persist. This could be either a JSON saved using file system or a Database. As the app matures we'll define it somewhere else
 * puppeteerPerformance.js

'use strict';

const chromeLauncher = require( 'lighthouse/chrome-launcher/chrome-launcher' );
const fs = require( 'fs' );
const lighthouse = require( 'lighthouse' );

const { APP_URL } = proccess.env;
// 1.

const flags = {
  output: 'json'

const launchChromeAndRunLighthouse = ( url, flags, config = null ) => {
  return chromeLauncher.launch()
    .then( chrome => {
      flags.port = chrome.port;
      return lighthouse( url, flags, config )
        .then( results =>
          .then( () => results )
    } );

// 2.
launchChromeAndRunLighthouse( APP_URL, flags )
// 3.
  .then( results => {
     fs.writeFile( './results.json', JSON.stringify(results), function ( err ) {
        if ( err ) {
          return console.log( err );
        console.log( 'The file was saved!' );
      } );

Enter fullscreen mode Exit fullscreen mode

Note that the results variable could be sent to a database and be stored for historycal comparison.

In this case, we'll just save it as a JSON file

2. Not Creating our Github Action

Bummer: at this time, Github actions are in public, beta, and I am on the wait list. So we will use a Github WebHook instead. If you are in a position to authorize my request, I'll be happy to blog about it.

NodeJS: Here is the repo with all the code.

I have already written a blog post on how to setup Github Webhooks. In this case I'll create a Heroku app in and use that url for the URL settup.

Now we need to create a simple Express Application that runs tests everytime a request is recieved.

We will install express

yarn add express
Enter fullscreen mode Exit fullscreen mode


const { APP_STAGING_URL, APP_PRODUCTION_URL } = process.env;

const express = require('express');
const bodyParser = require('body-parser');
const fs = require('fs');
const { lighthousePerfAudits } = require('./audits/lighthousePerfAudits');

const app = express();
const flags = {
  output: 'json',

app.use(bodyParser.json());'/run', (req, res) => {
  // 1. Check secret
  if (req.headers['x-hub-signature']) {
     * Secret is valid,
     * run tests and write json data
     * on both environments
    lighthousePerfAudits(APP_PRODUCTION_URL, flags)
      .then((results) => {
        fs.writeFile('/production_results.json', JSON.stringify(results), (err) => {
          if (err) {
            return console.log(err);
          console.log('The file was saved!');

    lighthousePerfAudits(APP_STAGING_URL, flags)
      .then((results) => {
        fs.writeFile('/staging_results.json', JSON.stringify(results), (err) => {
          if (err) {
            return console.log(err);
          console.log('The file was saved!');

    // send response with 200
  } else {
  // secret is not valid, return 500

app.listen(process.env.PORT || 8080, () => {
  console.log('App linstening on ', process.env.PORT || 8080);

Enter fullscreen mode Exit fullscreen mode


With this instance in place, we can run scripts everytime a push is deployed to the repository and get our relevant metrics in order.

There are some lose ends on the application like:

  • Where should this data persist?
  • Is there a way to just plug it into Github?
  • How can we visualize the historic data of our releases performance?
  • What does the fox say?

I'll address those concerns in further posts. I'm also working on an openSource SaaS that solves this questions. You can hit me up on twitter if you have more questions.

NodeJS: Here is the repo with all the code.


Further resources:

Discussion (0)