Never used a type system before or just new to Flow? Let's get you up and running in a few minutes.
Have a question about using Flow? Check here first!
Learn how to add Flow type annotations to your code: Primitives, Objects, Functions, Classes, and more.
Define a fixed set of constants which create their own type. Exhaustively checked in switch statements.
Learn how the type system in Flow works: Subtyping, Variance, Refinements, and more.
How to use Flow from the command line. Including how to manage the Flow background process.
Flow tries to work out of the box as much as possible, but can be configured to work with any codebase.
Learn how to create and use library definitions for the third-party code your code depends on.
Learn how to write types in .flow files.
Learn how to suppress Flow's type errors.
Learn how to use Flow to effectively type common and advanced React patterns.
Detailed guides, tips, and resources on how to integrate Flow with different code editors.
Learn how to configure Flow's linter to find potentially harmful code.
Learn how to enable stricter type checking on a file-by-file basis.
© 2013–present Facebook Inc.
Licensed under the MIT License.