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Jérôme Pott
Jérôme Pott

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Building my first web extension

Since I've learned that web extensions speak the same languages as websites (HTML, CSS and JavaScript), I've always wanted to give it a try. This post is less a tutorial and more a summary of my experience.

Getting started

Getting started is indeed very easy:

I was able to quickly get something working, however, I also quickly faced some limitations that required me to set up a build pipeline in order to:

  • use npm modules
  • work with promises (browser APIs use callbacks)
  • have my extension automatically work both in Chrome and Firefox
  • have hot module replacement (HMR)
  • use Vue components and TailwindCSS
  • in short: have my dev environment as close a possible to my usual environment.

Fortunately, I found this awesome plugin that takes care of all the above-mentioned points.
This plugin scaffolds a web extension project structure and includes the essential webextension-polyfill.
All I had left to do with to set up TailwindCSS and I was ready to code.

Debugging web extensions

I didn't find how to use the Vue devtools extension for debugging, but in my case, logging to the console was sufficient.

To see the console logs when debugging the popup:

  • Chrome: Open dev tools, right-click inside the popup and select "inspect"
  • Firefox: Click the inspect button on the screen where you added your extension as a temporary extensions [image]

For the settings page, you can set options_page directly to options.html, which will open it as a full page.

You can also open the popup as a normal web page by typing its URL: chrome-extension://your_extension_id/popup.html

What about testing?

Thanks to the simplicity of Cypress, I've started to add tests to my projects. However, Cypress currently cannot visit web extension.

Then I found a great blog post about testing web extensions with Jest and Puppeteer. The showcased extension is even built with Vue.

Thanks to that post, I was able to quickly set up Jest. However, I quickly realized that the History API I was using was not mocked by the jest-webextension-mock library🙄

What I ended up doing is to only unit test the main functions with Jest. As fixtures for the tests, I exported a sample browsing history as JSON.

The post later mentioned E2E testing with Puppeteer. I tried to set it up but ran into errors from the Jest integration. At that point, I told myself that I shouldn't spend more time on that topic and move on to finally publishing my extension.

Publishing my extension

Chrome Web Store

The developer dashboard seemed to have recently been redesign. I found it very easy to navigate. There are many contextual info-bubbles that provide useful information. The whole process was very straightforward. I just had to fill out all the required information and pay the entrance fee of $5 to submit my extension for review. Two days later, it was published.

Link to Chrome store page:

Add-ons for Firefox

At Firefox, the submission process was also easy and the review also only took two days. Unlike Chrome, I had to upload the source code. I am actually surprised that Chrome didn't ask for it. Maybe paying the fee with a credit card number provided enough insurance.

Link to Firefox store page:

Now go build your own extension!

Don't fret too much about the fact that there are probably extensions that will be similar/better than yours. With that kind of thinking, you'll never get started. If this doesn't help, take it as a learning exercise.

See my extension: it tracks the time since the last visit to websites... There are plenty of apps that do a similar job and boast more features. But it solved a specific need I had and I use it daily.

You check its source code here:

Cover photo by Aron Visuals

Top comments (4)

harithzainudin profile image
Muhammad Harith Zainudin

Nice! Congrats on the web extension. The important thing is learning and become better. Like you said don't care about other similar extension in the market. I totally agreed with that. If not we are not going anywhere!

jessica000 profile image
Jessica Valencia

Great post!
I have one question. How do you embed DEV article in comments? I may want to refer to your article in my comments but I don't know how to.

mornir profile image
Jérôme Pott

Hey! Thanks for your comment!
Like this: {% link mornir/building-my-first-web-extension-4h71 %} 😉

jessica000 profile image
Jessica Valencia