Your license to use React.js can be revoked if you compete with Facebook

React is a popular JavaScript technology for creating rich user interfaces. It originates from Facebook (Instagram originally) and is widely used. The library is open sourced under BSD, but it comes with an added patent clause that you should be aware of.

If you are using or considering using React in a project you might want to consult a lawyer. Because of the patent clause you are not allowed to do anything that constitutes as competing with Facebook. If you do take legal actions or in other ways challenge Facebook, your license to use React is immediately revoked.

Your license is also revoked if you have any legal disputes if you have legal disputes with any other company using React. This is the reason why both Google and Microsoft employees are not allowed to use React.js in their work - according to Rob Eisenberg, creator of the Aurelia framework and a former member of the Angular 2 development team.

While this may be a theoretical impact for most implementation projects, it's certainly worth remembering and can limit some other projects like WordPress Calypso which have built a deep coupling to the library. Automattic, the company behind WordPress, is no stranger to petty litigation, but with Facebook they would likely be on the receiving end.

Many Open Source products like Drupal and WordPress are adopting Facebook technologies. It might be tricky when companies like Automattic with Open Source based products like WordPress.com maybe unable to leverage their userbase in the future in ways that could be considered as competition by Facebook.

This is a distant possibility now as Facebook is at the height of it's power, but like Yahoo! Facebook will fall back from grace some day. At that point the company might be interested in taking use of the power granted by the license in a competitive sense. So if you're looking to create a Facebook killer with React, you might want to call up your lawyer.

Remember that patent laws are enormously complex, especially in IP related matters they are often hard to interpret. As the feud between Google and Oracle over use of Java in Android shows, they can take years to handle. This means that you'll potentially need very deep pockets, even if you end up winning the case.

Here is the whole clause any developer using React.js in their projects agree to: