Flow is a great static type checker for JavaScript. Unfortunately it's design seems to assume that developers are slowly incorporating flow into large legacy code bases, instead of starting fresh. This means that each file needs to opt into type checking, otherwise obvious type errors may be missed.
NOTE: This package is deprecated in favor of the require-valid-file-annotation rule in eslint-plugin-flowtype.
This rule aims to enforce that all js files have the flowtype header comment, enforcing type checking across the project.
Examples of incorrect code for this rule:
// Missing flow header comment.
var hello = 'world';Examples of correct code for this rule:
// @flow
var hello = 'world';// @noflow
var hello = 'world';The rule also supports eslint --fix. It adds a // @flow line to the top
of files that don't have it already.
This rule is not appropriate when your project has a mix of plain (legacy) js with new flow typed js.