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Bootstrap a Reason-React project with Parcel

Posted on March 7, 2018·

Not that long ago I used Create-React-App a lot to quickly boostrap my React projects. That’s why I naturally used Reason Scripts when I wanted to use Reason-React. But even if I still understand the advantages of the approach of CRA and Reason Scripts, I recently discovered Parcel, a very minimalist bundler for web projects.

There are already a lot of articles explaining the advantages of Parcel, and how to use it with React for instance. What I wanted to do here is show you how you can use it to start a new project with Reason first, then add Reason-React to write React components.

TL;DR: I created a project on GitHub containing the final code for the article, if you just want to see the final result.

Start a basic Parcel project

First, let’s init a new project with Yarn (NPM should work just fine too) and add Parcel:

$ mkdir reason-parcel && cd reason-parcel
$ yarn init -y
$ yarn add --dev parcel-bundler

Let’s edit the generated package.json to add the start script:

{
  "name": "reason-parcel",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "scripts": {
    "start": "parcel public/index.html"
  },
  "devDependencies": {
    "parcel-bundler": "^1.6.2"
  }
}

Then let’s create our public/index.html file:

<html>
  <body>
    <script src="../src/index.js"></script>
  </body>
</html>

And finally let’s add a src/index.js file so we can test our first version:

console.log('Hello from JavaScript!')

To start the project, let’s just run yarn start:

Hello from JavaScript!

Add Reason

Okay this was basically the tutorial to start a Parcel project, but where is Reason? Let’s start by adding bs-platform dependency to the project:

$ yarn add bs-platform

We’ll need a bsconfig.json file to tell BuckleScript what to do:

{
  "name": "reason-parcel",
  "refmt": 3,
  "sources": "src",
  "dependencies": [],
  "package-specs": {
    "module": "commonjs",
    "in-source": true
  },
  "suffix": ".bs.js"
}

We are telling BuckleScript to compile Reason files to JavaScript in the same directory, with .bs.js, so our src/index.re will be compiled to src/index.bs.js. This way Parcel will be able to deal with them natively.

Let’s create this src/index.re file (by renaming src/index.js file to src/index.re) and set its content to:

Js.log("Hello from Reason!");

We also need to update our public/index.html with the new path of the main file, which is now written in Reason:

<script src="../src/index.re"></script>

Let’s start our app now:

Hello from Reason!

There it is! Only one command to run the project including Reason to JavaScript transpilation! 😁

Add Reason-React

Last step now: adding Reason-React to the project so you can write your components in Reason. First we need to add the dependency:

yarn add reason-react

We also need to update bsconfig.json to tell BuckleScript we’ll use Reason-React and JSX:

{
  "name": "reason-parcel",
  "refmt": 3,
  "sources": "src",
  "bs-dependencies": ["reason-react"],
  "reason": {
    "react-jsx": 2
  },
  "dependencies": [],
  "package-specs": {
    "module": "commonjs",
    "in-source": true
  },
  "suffix": ".bs.js"
}

Now let’s create a simple component in src/Greeting.re:

let component = ReasonReact.statelessComponent("Greeting");

let make = (~name, _children) => {
  ...component,
  render: (_self) =>
    <div>
      (ReasonReact.stringToElement("Hello "))
      <strong> (ReasonReact.stringToElement(name)) </strong>
      (ReasonReact.stringToElement("!"))
    </div>
};

Let’s use it in src/index.re:

ReactDOMRe.renderToElementWithId(<Greeting name="Sebastien" />, "root");

And finally let’s add a root div to our public/index.html to render our component:

<html>
  <body>
    <div id="root"></div>
    <script src="../src/index.re"></script>
  </body>
</html>

Wow that’s it! Easy right? Here is what you should get in your browser:

Hello from Reason!

Now you’re ready to use React to build powerful and maintainable components and enjoy the possibilities of Reason in the same time. Of course it isn’t the only way to do so, but I like how elegant the method with Parcel is.

I’d be curious to know if you see improvements to this workflow. Maybe using Parcel packagers or plugins could make it even cleaner? 😉

Some resources:

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