Getting Started with DEJA.js

DEJA.js (DCC-EX JavaScript API) is an open-source control system for model railroads. It connects your web browser to a DCC-EX CommandStation over USB serial, giving you real-time control of locomotives, turnouts, signals, sound effects, and more — all from a modern web interface.

Whether you run a small switching layout on your desk or a large club layout with multiple operators, DEJA.js provides the tools to control it from any device with a browser.

Four Steps to Running Trains

Getting started takes just a few minutes:

Sign Up — Create your free DEJA Cloud account with one click (Google, GitHub, or email).
Choose a Plan — Start with the free Hobbyist tier or pick a paid plan with a 14-day free trial.
Register Your Layout — Give your layout a name and you're configured.
Install & Run — Run one command to install the DEJA Server, connect your CommandStation, and go.

That's it. Once the server is running, open DEJA Throttle on any device and drive.

Head to the Quick Start guide for the full walkthrough.

How It Works

[DCC-EX CommandStation] --USB--> [DEJA Server] <--WiFi/LAN--> [Throttle App]
       (your hardware)          (your computer)               (any device)
                                      |
                               [DEJA Cloud]
                          (layout config & roster)

The DEJA Server is the only piece you install locally. It bridges your CommandStation over USB to the rest of the system. The Throttle, Cloud, and Monitor apps are hosted web apps you open in a browser.

Who Is DEJA.js For?

Model railroad hobbyists who want browser-based train control without installing desktop software.
Club operators who need multi-user access to a shared layout over a local network.
Tinkerers and makers who want to extend their layout with custom effects, sound, and automation using JavaScript and TypeScript.

No programming experience is required to use the apps. If you want to customize or extend the system, familiarity with TypeScript and Vue.js will help.

Pricing Plans

DEJA.js offers three tiers so you can start free and grow into the features you need:

	Hobbyist	Engineer	Conductor
Price	Free	$7/mo or $67/yr	$18/mo or $173/yr
Locomotives	5	25	Unlimited
Layouts	1	2	Unlimited
Turnouts, Signals, Effects	—	15 each	Unlimited
Tour App	—	—	Included

Paid plans include a 14-day free trial — no charge until the trial ends.

What's Included

DEJA.js is a suite of specialized applications that work together:

Apps

App	Purpose	Description
Throttle	Train control	The primary operator interface. Control locomotive speed, direction, and functions. Throw turnouts, activate routes, and trigger effects.
Cloud	Layout management	Configure your layout: manage your locomotive roster, set up turnouts and routes, wire signals, and define effects.
Monitor	System dashboard	A diagnostics and logging dashboard showing real-time system status, connected devices, and communication logs.
Tour	Interactive tours	Run scripted tours and effects sequences — useful for open houses, demonstrations, and automated layout operations. (Conductor plan)
Server	Backend bridge	A Node.js backend that bridges your browser apps to the DCC-EX CommandStation over USB serial.

There is also a Sound API (Next.js) that manages sound effect assets stored in Vercel Blob storage.

Shared Packages

The packages/ directory contains reusable libraries shared across apps:

@repo/modules -- Core business logic for locomotives, turnouts, effects, signals, and routes.
@repo/ui -- Shared Vue components (locomotive avatars, turnout switches, track power controls, and more).
@repo/dccex -- DCC-EX command protocol integration.
@repo/deja -- Core DEJA composable for writing commands to Firebase.
@repo/firebase-config -- Firebase client and admin SDK initialization.
@repo/auth -- Authentication and route guards.

Device Firmware

The io/ directory contains Arduino and Raspberry Pi Pico W firmware for hardware I/O boards that communicate with the server over MQTT.

System Requirements

Before you begin, make sure you have:

Node.js 22 or later
pnpm 9 or later
Git for cloning the repository
A DCC-EX CommandStation connected via USB
A USB cable connecting the CommandStation to your computer

Confirm Node.js is ready: node --version should print v22.x.x or higher.

Next Steps

Ready to get running?

Quick Start -- Sign up, install, and drive your first train in minutes.
Installation -- Detailed setup for developers who want the full monorepo experience.
Architecture -- Understand how the system is structured and how data flows between components.