React.js is a JavaScript library. It was developed by engineers at Facebook.
Here are just a few of the reasons why people choose to program with React:
- React is fast. Apps made in React can handle complex updates and still feel quick and responsive.
- React is modular. Instead of writing large, dense files of code, you can write many smaller, reusable files. React's modularity can be a beautiful solution to JavaScript's maintainability problems.
- React is scalable. Large programs that display a lot of changing data are where React performs best.
- React is flexible. You can use React for interesting projects that have nothing to do with making a web app. People are still figuring out React's potential. There's room to explore.
- React is popular. While this reason has admittedly little to do with React's quality, the truth is that understanding React will make you more employable.
JSX is a syntax extension for JavaScript. It was written to be used with React. JSX code looks a lot like HTML.
What does "syntax extension" mean?
In this case, it means that JSX is not valid JavaScript. Web browsers can't read it!
If a JavaScript file contains JSX code, then that file will have to be compiled. That means that before the file reaches a web browser, a JSX compiler will translate any JSX into regular JavaScript.