flow-webpack-plugin

1.2.0 verified Sat Apr 25 auth: no javascript

A webpack plugin that invokes the Flow type checker during each webpack compilation. Current version 1.2.0 is stable and actively maintained. It allows Webpack to exit with non-zero return codes if Flow validation fails, supports watch mode, and can reuse a project's existing flow-bin installation without requiring Flow to be on $PATH. Unlike per-file type-checkers, it runs Flow on the entire project.

Common errors

error TypeError: FlowWebpackPlugin is not a constructor ↓

cause Using ES module import or destructuring require.

fix

Use const FlowWebpackPlugin = require('flow-webpack-plugin'); then new FlowWebpackPlugin(...)

error Error: Cannot find module 'flow-bin' ↓

cause flow-bin not installed and no flowPath option provided.

fix

Install flow-bin: npm install --save-dev flow-bin, or configure flowPath to a Flow binary.

error Flow returned exit code X but webpack continues ↓

cause failOnError or failOnErrorWatch not set to true.

fix

Set failOnError: true (or failOnErrorWatch: true for watch mode) in plugin options.

Warnings

gotcha flow-webpack-plugin does not provide ES module exports; attempting to import with ESM syntax will fail. ↓

fix Use CommonJS require: const FlowWebpackPlugin = require('flow-webpack-plugin');

gotcha The failOnError option defaults to false; flow errors will not cause webpack to exit with non-zero code unless explicitly set. ↓

fix Set failOnError: true in options to make webpack compilation fail on Flow errors.

gotcha If flow-bin is not installed, the plugin will throw unless flowPath option provides an alternative path. ↓

fix Ensure flow-bin is installed as a devDependency or provide a valid flowPath option.

Install

npm install flow-webpack-plugin

yarn add flow-webpack-plugin

pnpm add flow-webpack-plugin

Imports

FlowWebpackPlugin
wrong
```
import FlowWebpackPlugin from 'flow-webpack-plugin'
```
correct
```
const FlowWebpackPlugin = require('flow-webpack-plugin')
```
The package does not provide ES module exports; CommonJS require is required. There is no default or named import.
FlowWebpackPlugin
wrong
```
const { FlowWebpackPlugin } = require('flow-webpack-plugin')
```
correct
```
const FlowWebpackPlugin = require('flow-webpack-plugin')
```
The export is a single constructor function, not a named export. Destructuring will result in undefined.
Configuration options
wrong
```
new FlowWebpackPlugin({ failOnError: 'true' })
```
correct
```
new FlowWebpackPlugin({ failOnError: true, flowPath: require('flow-bin') })
```
failOnError and failOnErrorWatch are boolean; passing string 'true' will be truthy but incorrect.

Quickstart

Example webpack configuration enabling Flow type-checking with error-on-fail settings.

const FlowWebpackPlugin = require('flow-webpack-plugin');

module.exports = {
  plugins: [
    new FlowWebpackPlugin({
      failOnError: true,
      failOnErrorWatch: false,
      reportingSeverity: 'error',
      printFlowOutput: true,
      flowPath: require.main.require('flow-bin'),
      flowArgs: ['--color=always'],
      verbose: false
    }),
  ],
};