Tired of having to run your code to find bugs? Flow identifies problems as you code. Stop wasting your time guessing and checking.

Flow is a static type checker for your JavaScript code. It does a lot of work to make you more productive. Making you code faster, smarter, more confidently, and to a bigger scale. Flow …

Learn how to add Flow type annotations to your code: Primitives, Objects, Functions, Classes, and more. 📄️ Type System. In JavaScript there are many types of values: numbers, strings, …

Babel is a compiler for JavaScript code that has support for Flow. Babel will take your Flow code and strip out any type annotations. If you already use Babel in your project, see using Babel. …

Classes in Flow are just like normal JavaScript classes, but with added types. Class Methods Just like in functions, class methods can have annotations for both parameters (input) and returns …

Developers will often use Flow and React together, so it is important that Flow can effectively type both common and advanced React patterns. This guide will teach you how to use Flow to …

^ Cannot return `x` because number [1] is incompatible with string [2]. [incompatible-return] References:

JavaScript includes a Map class, but it is still very common to use objects as maps as well. In this use case, an object will likely have properties added to it and retrieved throughout its lifecycle.

Oct 13, 2016 · One of Flow's original goals was to be able to understand idiomatic JavaScript. In JavaScript, you can call a function with more arguments than the function expects. Therefore, …

For most new Flow projects, you will follow this general pattern: Initialize your project with flow init. Start the Flow background process with flow. Determine which files Flow will monitor with // …