You should learn JavaScript first. After that you will get an answer to your question.

Laravel already provides support for React or Vue out of the box. So you need not worry much about the integration part. Just go about learning what interests you. Rest can be found here:

laravel.com/docs/5.6/frontend

Learning React or any other front-end technology (be it a framework or a library) has nothing do with the choice of your backend. All of them have their pros and cons, so yes, you can learnt React and hook it up with a Laravel backend.

Do it! ReactJS is a great library to do powerful and complex state management, and Laravel is a great server-side platform to work from.

Laravel comes bundled with Vue, but you can easily switch to React by using the following command line once Laravel is installed:

php artisan preset react

And here's a tutorial that covers some of the basics if you'd like to understand the ecosystem (Laravel Mix and all that jazz).