### Primary keys and clustered indexes

Primary keys and clustered indexes are two distinct concepts that often get mixed up with one another, but it’s important to understand the difference between them in order to build robust, performant SQL databases.

Linting is essential to writing good JavaScript, and ESLint is, for my money, the best JavaScript linter out there at the moment. It’s super flexible, and also has plugin support which allows for features like ReactJS linting. For those starting a new ReactJS project, or those who want to integrate ESLint into an existing one, here is an .eslintrc (configuration) file to get you started.