Posts with the tag: javascript

The best of ESLint

Have you ever asked yourself how ESLint works and what we can do with it? Why do we have so many rules, and which are the best and most helpful? In this post, you will learn one thing or two about this linter and its rules.

Overriding specific console messages in Jest

Learn how to override specific console.log and other console messages in Jest

Creating a dynamic map in the edge

Learn how to use Vercel Edge Middleware in Next.js and create a cool world map with your visitor location

Building TypeScript definitions on demand

I recently came across an interesting problem: is it possible to dynamically create TypeScript definitions for a React component library that doesn't use TypeScript at all? Something like a DefinitelyTyped package for a private NPM package?

The undocumented Lighthouse guide

Lighthouse is the go-to tool for improving the quality of web pages. Lately, I have been using Lighthouse a lot at work to identify opportunities for performance optimizations. This post is part of a 6 part series that I have written about how to get the most out of Lighthouse.

My experience using Lighthouse in the real world

Lighthouse has been part of my daily work for the last few months and I shared some snippets in my last few posts. For this particular post, it is time to share how I am using Lighthouse in a product used by millions of people and what I have discovered during this process.

Generating Web Vitals information with Lighthouse

Earlier this year, Google announced that “page experience” would impact its search ranking. A few weeks ago, they announced that the new page experience signals will roll out in May 2021. But what are these page experience signals?

Getting asset transferred information with Lighthouse

Have you ever about thought tracking what is added to a page or web app? Did not know how your website became 15MB? Sounds like it is time to track this data!

Generating screenshots with Lighthouse

Lighthouse captures the rendering timeline of a page in 10 images. Do you need to store them? If yes, keep reading in order to learn how to store these images.

Creating HAR files with Lighthouse

HAR (HTTP Archive) is a JSON file containing all information about a browser’s interactions with a page. This file is often used for performance analysis. Earlier this year, I shared what kind of information we can get from and today we will automate the HAR creation.

Automating accessibility tests with Cypress

In my previous post, I covered how to add screenshot testing in Cypress to ensure components unintentionally change over time. Now, I will share how to automate accessibility tests with Cypress.

Adding screenshot testing with Cypress in your project

Developers are usually concerned about the quality of their code. There are different kinds of tests to avoid breaking code when a new feature is added in a project, however, what can be done to ensure that components don't look different over time?

Creating your own ESLint config package

ESLint is a powerful tool to enforce consistent coding conventions and ensure quality in your JavaScript codebase. Coding conventions are sometimes difficult to decide and having a tool to automate enforcement is great to avoid unnecessary discussions. Ensuring quality is also a welcoming feature: linters are excellent tools for catching bugs, such as those related to variable scope.

Changing node versions automatically per directory

Working in multiple Node projects sometimes means using different versions of Node. nvm is one popular solution for Linux, macOS and Windows WSL that handles multiple Node installations. One of its most unknown tricks is the deeper shell integration. Check the video:

Using Dependabot to keep your environment up to date

Adding dependencies in a project is seen as a good way to not reinvent the wheel but at the same time it can be concerning in many different aspects:

Exploring device detection for better user experiences in 2020

A few months ago I watched a great talk in Chrome Dev Summit about performance in slow devices.

Creating a website for my Apple Collection

Part of the collection

A while ago I started an Apple Collection. After a few laptops and a few iDevices, I decided that I should start collecting info about my iThings. In the beginning, I created a gist containing model, serial number, how did I get the device, minimum/maximum OS, etc.

The list kept going bigger and bigger and the content started looking messy. The natural way to organize my data would be inside a SQL database, with the information distributed in columns. After organizing the information in tables, I would create a graphQL API (the one cool kids use these days) to give me the data needed to populate my UI – probably written in React, compiled with Babel and packed with webpack.

Forcing the usage of yarn (and at a specific version)

People and organizations often have preferences for a specific package manager. At work, we decided to use Yarn due to emoji support (jk) but how to keep everybody using Yarn? 

We can use the preinstall hook to check if the user run npm installor yarn install. Here is one example:

Disabling autofill in Chrome

Autofill in form elements is a very useful feature in browsers. Creating new accounts or shopping in an online store are examples of this feature saving us time.

However, the autofill feature can be a problem for SaaS products. Imagine that you want to edit the email address of one of your users. You hit edit in one screen and once you get a form with your user data Chrome will replace their email to your email. This is not a good user experience.

MDN has an article showing “How to turn off form autocompletion”. The solution is using the autocomplete attribute with an off value. This doesn't work in Chrome.

Digging in Stackoverflow and Google results, I found a bug issued in 2015 about the topic. Here is the TL,DR (from March 2016):

Thoughts on building components libraries

A few months ago we started using React at Thinkific. One of the challenges of using React is creating reusable components not only from a look and feel perspective but also shareable in different projects.

I didn't create this concept of elements (or components) library. To be honest, there are podcasts, courses, and examples everywhere about it but how to even start it? When you start creating a project from scratch you face several questions:

  • How to style components? Sass? Stylus? styled-components?
  • How to show the elements?
  • How to build the library? Babel? Webpack?
  • How to publish the library? To NPM or not NPM?
  • How to use integrations and CI in your favour?

Lots of decisions and you may not know all the answers. Startup Life™ doesn't let you do whatever you want – everything has a cost and a trade-off. Why am I talking all this story? Because I wanted to share my thoughts about it and I created a repository to document what we are doing.

iPhone e Rails

O desenvolvimento de web apps para iPhone requer alguns cuidados especiais. Em nossas aplicações significa pensar em um layout para o gadget. Uma forma rápida de definir o layout para iPhone é através do código abaixo:

jQuery no Spotlight

Anteriormente eu postei sobre como integrar a documentação do Ruby e do Rails no dicionário do Mac OS, que automaticamente é indexado pelo Spotlight.

Bookmarklet para ver propriedades dos elementos de uma página

O XRAY é um bookmarklet para Safari e família Mozilla que mostra as características de determinado elemento de uma página. Para quem usa Firefox, o XRAY lembra a função Inspect da extension Firebug. Recomendado!

Novas janelas em Javascript não-obstrusivo

A newsletter dessa semana do SitePoint mostrou uma forma bem interessante de abrir novas janelas com javascript não-obstrusivo e validando XHTML Strict (para quem não sabe, o atributo ‘target' da tag ‘a' não passa na validação).

12 efeitos bacanas com

Criar efeitos visuais em Javascript era algo bem complexo. Muitos efeitos da lista que cito abaixo era algo somente imaginável para criar, para mim, no Flash. Entretanto, as coisas mudaram. O é uma biblioteca que permite a criação de efeitos de forma super-simples, sem requerer conhecimentos jedi em JS. Vamos a lista então:

  1. Image Gallery – Efeitos suaves e bem feitos
  2. Reflector – Imagens com reflexos (muito usado no site da Apple)
  3. Newsticker – Newsticker não-obstrusivo
  4. Auto-Completer – Estilo Google Suggest
  5. Auto-Completer – Demo do wiki do


Há pelo menos 2 anos, falei dos bookmarklets, Javascripts que modificam o comportamento do navegador. Talvez eles seriam o avó do Greasemonkey, que prometem algo semelhante, mais com uma maior riqueza e poder.

Greasemonkey para orkut na Faculdade

O sysadmin lá da faculdade barrou, no servidor, o acesso à Coitado, ele esqueceu da URL, via SSL.