Why is React a library and not a (simple) framework?

The correct definition that provides the difference between the library and the framework and the only one that makes sense :

"Your code calls library whereas framework calls your code."

Only this definition existed before unscrupulous React promoters started to promote it as a library.

React is obviously the framework. Very complex and opinionated one.

The litmus test:

• If your code calls it, it's a library.
• If it calls your code, it's a framework.

Looking at the React tutorial Starter Code ReactDOM.render() is the only part of React that your code calls. The rest, i.e. the majority of your code, is called by React.

Ipso facto - React is a framework because it is in control when most of your code runs.

For the expanded argument see: React is a (view component) framework

For me, Angular is a framework - it's highly opiniated makes implicit assumption about your code and when there's a problem, you get a cryptic error message such as

'Unexpected value 'undefined' declared by the module 'DynamicTestModule' with a stack trace as high as a building entirely located inside Angular itself.

React is a library because you plug it into the part of your code you want, it is checking its input correctly and is focusing on doing one thing and doing it good instead of trying to do everything the bad way.

It's definitely NOT a framework. Something like "Create React App" or "Meteor" are frameworks that use React, but React on it's own does not run, it doesn't really do anything by itself. It needs Webpack or Rollup and all kinds of other tooling just to get up and running. React is a view library, that has an approach, but that's it. Frameworks are complete puzzles, React is just a piece of the puzzle.

I think we've heard all the arguments by now. Let me ask a question instead: does it really matter if React is a library or a framework? What are the consequences?

I think you confuse react with the whole ecosystem around it.

A framework covers the edges, whereas a library is a tool to fulfill certain tasks. React itself only handles one task: abstracted Web Components. It provides an internal state, lifecycles and external properties and with ReactDOM a renderer for a browser or similar environment - and nothing more.

This has a few advantages: it is smaller than a full-featured framework, is less opinionated on how to solve problems and therefore allows for more choice. Don't like react-router? Use another one - or no router at all, if you don't need any. Need a complex state management? Try redux. Need to handle side-effects? you can choose between redux-thunks, redux-sagas and redux-observables. Unit testing can be done with enzyme, jest or mocha, sinon, chai, jasmine, karma, etc. There's no one or best way to do it, so you can do whatever works best for you.

In my opinion React is a library. It does one thing, it let you describe how one piece of the interface should look like.

The interesting thing is that people choose to use it as a framework, by reaching out to other packages in the react ecosystem. What ends up happening is that your code lives inside React.

Take a look at this examples
React as a framework
React as a library

I am of the opinion that react (the package) is, in fact, a library. However, React as a whole has become a large ecosystem which is almost indistinguishable from a framework. While it is possible to use react as a library, in practice, one actually adopts a large number of tools and libraries from the React ecosystem. How many applications are there really that just use react without any related tooling or libraries?

The very fact that the default way of using react involves the use of a specialized DSL that isn't valid Javascript (JSX) tells me that no, React is not just a humble library. Is it a framework, though? Technically, probably not. However, the end result doesn't feel that different.

It reminds me a bit of the relationship between Ruby and Rails. While yes, technically, you can use Ruby without Rails, how many people actually do?

Well there's react as in npm install react but that's not the same thing as the react you see on SO or job boards "React developer wanted" or "How do you filter an array in react?"