An Introduction to Rome: Facebook’s Experimental JavaScript Toolchain

On February 27, 2020, Facebook open‑sourced Rome, an experimental JavaScript toolchain created by Sebastian McKenzie, the author of Babel and Yarn and a member of the React Native team. Before becoming an official Facebook project, Rome was essentially McKenzie’s personal project.

Rome’s repository is located at https://github.com/facebookexperimental/rome . The project has undergone several name changes: it started as Sonic in 2016, then became Hydra , and finally was renamed Rome in March 2019, referencing the many metaphors associated with the city of Rome.

According to the project description, Rome is an experimental JavaScript toolchain that includes a compiler, linter, formatter, bundler, and test framework, aiming to become a comprehensive solution for handling JavaScript source code. All components are written from scratch in TypeScript, have no third‑party dependencies, and are organized as internal packages within a single monorepo.

Key Features

All tools are self‑hosted and can compile themselves.

Supports JSX, Flow, and TypeScript annotations.

Current focus is on linting (see issue 20 ).

Command‑Line Interface

Rome provides a rich set of commands, grouped by purpose:

Source‑code commands

analyzeDependencies : Analyze and output a file’s dependencies.

bundle : Bundle JavaScript into a single file.

compile : Compile a JavaScript file.

develop : Start a web server.

parse : Parse a file and output its AST.

resolve : Resolve a file path.

Code‑quality commands

ci : Install dependencies, run linter and tests.

lint : Run the linter on a set of files.

test : Execute tests.

Process‑management commands

restart , start , status , stop , web

Project‑management commands

config , publish (TODO), run (TODO)

Internal commands

evict : Evict a file from the memory cache.

logs

rage

Example Usage

A minimal example shows how a module export is transformed during bundling:

export const myVar = 'hello';

Another module imports this export:

import { myVar } from './moduleA.mjs';

Running the bundler:

rome bundle module.mjs dist

The generated bundle wraps all modules in a single closure, similar to Rollup, rather than creating a separate closure per module as Webpack does.

Running Rome

Because Rome has not been published to npm, you must build it from source:

git clone [email protected]:facebookexperimental/rome.git

cd rome

scripts/dev‑rome --help

These commands display the full help output, listing all available flags and sub‑commands.

References

Rome project: https://github.com/facebookexperimental/rome

Announcement article: https://jasonformat.com/rome-javascript-toolchain/

Twitter thread on the name change: https://twitter.com/sebmck/status/1108408813864906752