Create a Custom GitHub Action in Typescript

GitHub Actions are a powerful tool to automate your workflow. They can be used to run tests, deploy your code, publish a package, and much more.

The cool thing is, there's a GitHub Actions Marketplace where you can find a lot of actions created by... the community.

But what if you can't find the action you need? You can create your own and publish it there!

How to use this tutorial

The full tutorial (all chapters at once) is also available as a video, which you can find here:

Chapter 1: Building an MVP

Let's begin with an MVP (Minimum Viable Product) of our GitHub Action.

We'll start simple with an action having only the required parts to understand the basics, then we'll add more features to it.

Action Definition

The definition is stored in the action.yml file, put directly in the root of the repository.

name: 'My Custom Action'
description: 'Say Hello'
author: 'Leonardo Montini'

runs:
  using: 'node16'
  main: 'dist/index.js'

The most minimal action definition is composed of a name and a runs object to define how the action is executed and what file to run. description and author are optional.

In case your action has some inputs, they will be defined in the action.yml file as well, in the inputs object.

inputs:
  name:
    description: 'The name of the person to greet'
    required: true
    default: 'World'

When publishing the action to the store, you might want to customize the appearance of the action in the marketplace. This can be done by adding a branding object to the action.yml file.

branding:
  icon: 'activity'
  color: 'green'

Anyway, for this MVP the first snippet will be enough.

Project setup

Let's create an empty node project with npm init -y.

You can now open package.json and add the build script.

{
  "scripts": {
    "build": "tsc"
  }
}

Since we want to use Typescript, we'll need to install it as a dev dependency.

npm install -D typescript

Then we'll create a tsconfig.json by running npx tsc --init and we'll edit it to match our needs.

{
  "compilerOptions": {
    "target": "ES2019",
    "module": "commonjs",
    "outDir": "lib",
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "strict": true,
    "skipLibCheck": true
  }
}

Project code

We can now create the src/index.ts file and start writing our action.

console.log('Hello World!');

We're building an MVP, right? So let's keep it simple for now and focus on all the required steps. We'll have time to expand it later.

Building the action

We can now build the action by running npm run build which will execute the tsc command as we defined in the package.json file.

This will create a dist folder containing the compiled code.

dist
└── index.js

In case you see index.js generated in the root of the project or inside src/, you might want to add make sure the outDir option to the tsconfig.json file is properly set to dist.

Creating the repository

In case you haven't done it yet, it's time to create a git repository as we'll need to push our code to GitHub soon.

git init

Don't forget to add a .gitignore file to the project to avoid committing files that shouldn't be tracked by git, for example, the node_modules folder.

A quick way to do it is by running npx gitignore node which will create a .gitignore file with the most common entries for a node project.

Note: in this particular case we want to push the dist folder to GitHub, so we'll need to remove the dist entry from the .gitignore file.

git add .
git commit -m "Initial commit"
git remote add origin
git push -u origin main

Closing

And that was it for today! if you have any question or suggestion, feel free to add a comment :)

See you in the next chapter!

Thanks for reading this article, I hope you found it interesting!

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Leonardo MontiniFollow

Awarded GitHub Star in 2023 ⭐️ I talk about Open Source, GitHub, and Web Development. I also run a YouTube channel called DevLeonardo, see you there!