Installation

Notes

With the instructions below, our new standard libraryReScript Core will be included by default. (In ReScript 11, it comes as a separate npm package@rescript/core. In future versions, it will be included in therescript npm package itself.)

Prerequisites

• Node.js version >= 14

• One of the following package managers:

  • npm (comes with Node.js)

  • yarn (yarn versions >1 need to setnodeLinker: node-modules in.yarnrc.yml)

  • pnpm

  • bun

New Project

The fastest and easiest way to spin up a new ReScript project is with thecreate-rescript-app project generator. You can start it with any of the aforementioned package managers ornpx.

npm create rescript-app@latest

• Follow the steps of the setup.

• Trigger a ReScript build:

  SH
  npm run res:build

• If you selected the "basic" template, simply run it with:

  SH
  node src/Demo.res.mjs

That compiles your ReScript into JavaScript, then uses Node.js to run said JavaScript.

When taking your first steps with ReScript, we recommend you use our unique workflow of keeping a tab open for the generated JS file (.res.js/.res.mjs), so that you can learn how ReScript transforms into JavaScript. Not many languages output clean JavaScript code you can inspect and learn from! With ourVS Code extension, use the command "ReScript: Open the compiled JS file for this implementation file" to open the generated JS file for the currently active ReScript source file.

During development, instead of runningnpm run res:build each time to compile, usenpm run res:dev to start a watcher that recompiles automatically after file changes.

Integrate Into an Existing JS Project

If you already have a JavaScript project into which you'd like to add ReScript you can do that in the following ways:

Quick Setup

In the root directory of your project, execute:

npm create rescript-app@latest

create-rescript-app will tell you that apackage.json file has been detected and ask you if it should install ReScript into your project. Just follow the steps accordingly.

Manual Setup

• Install ReScript locally:

  npmyarnpnpmbun

  npm install rescript @rescript/core

• Create a ReScript build configuration file (calledrescript.json) at the root:

  JSON
  {"name":"your-project-name","sources":[{"dir":"src",// update this to wherever you're putting ReScript files"subdirs":true}],"package-specs":[{"module":"esmodule","in-source":true}],"suffix":".res.js","bs-dependencies":["@rescript/core"],"bsc-flags":["-open RescriptCore"]}

  SeeBuild Configuration for more details onrescript.json.

• Add conveniencenpm scripts topackage.json:

  JSON
  "scripts":{"res:build":"rescript","res:dev":"rescript -w"}

Since ReScript compiles to clean readable JS files, the rest of your existing toolchain (e.g. Babel and Webpack) should just work!

Helpful guides:

• Converting from JS.

• Shared Data Types.

• Import from/Export to JS.

Integrate with a ReactJS Project

To start arescript-react app, or to integrate ReScript into an existing ReactJS app, follow the instructionshere.