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Single-player 🏀 and 🏈 management simulation games, made entirely in client-side JavaScript.
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Basketball GM and Football GM

Single-player sports simulation games. Make trades, set rosters, draft players, and try to build the next dynasty, all from within your web browser. The games are implemented entirely in client-side JavaScript, backed by IndexedDB.

Copyright (C) Jeremy Scheff. All rights reserved.

This project is NOT open source, but it is also not completely closed. Please see for details.

Development Info

If you just want to play the game, go to or Instructions below are for developers who want to run a copy locally so they can make changes to the code.

If you want to contribute but get stuck somewhere, please contact me! I'm happy to help.

License and Contributor License Agreement

This project is NOT open source, but it is also not completely closed. Please see for details.

If you want to contribute code to this project, you must sign a contributor license agreement. There are separate forms for individuals and entities (such as corporations):

Make a copy of the form, fill in your information at the bottom, and send an email to with the subject line, "Contributor License Agreement from YOUR_NAME_HERE (GITHUB_USERNAME_HERE)".

Step 1 - Installing

First, make sure you're using Node.js v6 or higher, older versions probably won't work. Then, all of the tooling used in development can be set up by simply installing yarn and running


from within this folder.

Step 2 - Building

To build the app along with all its assets, run

yarn run build

However during development, you probably would rather do

yarn run start-watch

which will start the server and watch JS and CSS files for changes and recompile. This simply runs both yarn run start and yarn run watch together, which alternatively can be run separately if you wish.

By default this will build the basketball version of the game. For football, set the SPORT environment variable to "football", like:

SPORT=football yarn run start-watch

Open package.json to see all available development scripts.

Step 3 - Running

To run the game locally, you need some way of running a web server to display the content. There are currently two ways to do it. It doesn't matter which you use as long as you can get it to run on your computer.

1. Node.js (easiest)


yarn run start

and point your browser to http://localhost:3000/. If you use the command yarn run start-watch from above, then running the command yarn run start is not necessary.

2. Apache

The mod_rewrite rules in .htaccess let the game run in Apache. Everything should work if you point it at the build folder with mod_rewrite enabled.

Service worker

A service worker is used for offline caching. This can make development tricky, because if you load the game in your browser, make a change, wait for build/watch to finish, and then reload... you will not see your change because it will cache the original version and then not update it on a reload. This is the normal behavior for service workers (they only switch to a new version when you actually close the website and reopen it, not on a reload), but it makes development annoying.

To work around that, in Chrome you can use the "Update on reload" option and keep your devtools open. Then reloading will always get you the latest version.

Even with that, ctrl+shift+r may be a good idea to make sure you're seeing your latest changes.

Step 4 - Testing

ESLint, Flow, and, stylelint are used to enforce some coding standards. To run them on the entire codebase, run

yarn run lint

Integration and unit tests are bunched together in the js/test folder. Coverage is not great. They can be run from the command line in Karma with

yarn test


yarn run test-watch

Code Overview

This is a single-page app that runs almost entirely client-side by storing data in IndexedDB. The core of the game runs inside a Shared Worker (or a Web Worker in crappy browsers that don't support Shared Workers), and then each open tab runs only UI code that talks to the worker. The UI code is in the src/js/ui folder and the core game code is in the src/js/worker folder. They communicate through the toUI and toWorker functions.

The UI is built with React and Bootstrap.

In the worker, data is ultimately stored in IndexedDB, but for performance and cross-browser compatibility reasons, a cache (implemented in src/js/worker/db/Cache.js) sits on top of the database containing all commonly accessed data. The idea is that IndexedDB should only be accessed for uncommon situations, like viewing stats from past seasons. For simulating games and viewing current data, only the cache should be necessary.

The cache is overly complicated because (1) the values it returns are mutable, so you better not mess with them accidentally, and (2) when you do purposely mutate a value (like updating a player's stats), you need to remember to always write it back to the cache manually by calling idb.cache.*.put.

Also in the worker, there is a global variable self.bbgm which gives you access to many of the internal functions of the game from within your browser.

Git Workflow

If you want to contribute changes back to the project, first create a fork on GitHub. Then make your changes in a new branch. Confirm that the tests (hopefully including new ones you wrote!) and ESLint all pass. Finally, send me a pull request.

It's also probably a good idea to create an issue on GitHub before you start working on something to keep me in the loop.

Less Important Development Info

Sport-specific stuff

Abbreviations of stats should be done like and stat pages. For instance, "defensive rebounds" is "drb".

Thank you BrowserStack

Shout out to BrowserStack for helping with cross-browser testing.

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