Flow: A Static Type Checker for JavaScript

Facebook developed and maintains Flow. The package provides static typing to normally late-bound JavaScript code, including React code. It provides this analysis to a JavaScript application, even if it is an existing application. Flow operates by carrying out a static abstract syntax tree (AST) analysis of type flows at build time.
Usage
Let’s kick the tires. Add a small annotation in a comment at the top of a source file:

Link: https://dzone.com/articles/flow-a-static-type-checker-for-javascript?utm_medium=feed&utm_source=feedpress.me&utm_campaign=Feed%3A+dzone%2Fwebdev