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Contributing to Ohm

Interested in contributing to Ohm? Great! Here are some tips to help you get started.

Getting Started


To develop Ohm, you'll need a recent version of Node.js.

Basic Setup

First, clone the repository:

git clone

Then, install the dev dependencies:

cd ohm
npm install

Note: the postinstall script (which is automatically run by npm install) will install a git pre-commit hook. See here for more information.

Useful Scripts

  • Use npm test to run the unit tests.
  • npm run test-watch re-runs the unit tests every time a file changes.
  • npm run build builds dist/ohm.js` and dist/ohm.min.js. which are stand-alone bundles that can be included in a webpage.
  • When editing Ohm's own grammar (in src/ohm-grammar.ohm), run npm run bootstrap to re-build Ohm and test your changes.

Doing Development

See our recommended Git workflow.

Pre-commit Checks

When you run npm install in an Ohm checkout, it will automatically install a pre-commit hook into .git/hooks/pre-commit. Every time you commit to the repository, the pre-commit script checks that all tests pass, and that the code passes a lint check. We use ESLint, which helps prevent many common programming errors, and ensures that the code follows a consistent style.

Usually, you should deal with a lint error by fixing the code so that ESLint no longer complains about it. However, there are a few cases where it makes sense to disable the error:

  • If you added new console.log statement, and you are sure that it is actual useful, you can disable the warning like this:

    console.log('a useful message');  // eslint-disable-line no-console
  • If you need to introduce a global variable (are you sure?), see the ESLint documentation on specifying globals.

If you need to temporarily commit something that doesn't pass the checks, you can use git commit --no-verify -- but use this sparingly!


To version and publish the ohm-js package, run the following in the ohm-js directory:

yarn version-package
yarn publish
git push && git push --tags