What the fuck is React?
You gotta hand it to Facebook for great branding - they knocked it out of the park when they created and named React. React or ReactJS is a Javascript library for the front-end or browser. Its claim to fame and uniqueness is that it’s reactive to data changes (hence the name). Whereas other tools and libraries required you to proactively change the interface elements when data changed, React was built to react to data changes and update the interface automatically.
There are a number of reactive type libraries and frameworks available (like Angular and Vue). React is unique in the flexibility and lack of configuration it requires. This means a programmer can pick any number of other libraries and tools to extend and enhance the target application. This flexibility means that there are many inventive ways to do the same thing, which of course leads to a lot of reinventing the fucking wheel. The downfall is there are so many options, it’s hard to be able to quantify what ‘experience with React’ really means. One React project can look vastly different than another.
React is pretty fucking popular with open source projects. But it’s not solely limited to open source projects. It also spawned a number of toolsets like React Native, which is mobile application programming but using React as the programming language.
While React is a library on top of Javascript, it’s likely that a programmer who knows React knows Javascript. However, as with all this shit, there are times when a React developer is so steeped in that discipline, that they just shit the bed when it comes to writing regular Javascript.