Should I learn TypeScript before react?
No. You don’t need to learn Typescript to use React.
Neither of these are at all connected. In reality, combining TypeScript with React can be difficult since, unlike Angular and TypeScript or Vue and TypeScript, they were not necessarily designed with each other in mind, since Facebook, and thus React's key proponents, use Flow as their primary "gradual typing" solution. However, there is a nice chunk of community interest, so it should not be impossible.
Why should you learn TypeScript?
Code that is much more predictable and simpler to debug. TypeScript provides the required safeguards for organizing the code and catching errors of all kinds before they are executed.
Static types allow some fantastic tools. Tools for improving the development experience by the code uniformity and quality, as well as saving development time. TSLint, tsserver—which is incorporated into most TS-enabled editors and awesome-typescript-loader are examples of such tools.
Harmonious teamwork on a growing codebase. Via well-defined interfaces, it combines code and introduces structure.
The key reason to learn TypeScript is code completion and familiarity for Java and C# developers. All of the other touted benefits are either exaggerated or, in my opinion, outweighed by the drawbacks.
Unit tests are more effective than typing at removing errors, and they must also be written while using Typescript.
Big projects require modularity rather than typing. Typescript will make it easier to build large inheritance trees that will land you in hot water. It's a different kind of trouble than with vanilla js, but it's always trouble.