A webpack plugin allowing to call Flow type checker during each webpack compilation.

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3661.2.06 years ago7 years agoMinified + gzip package size for flow-webpack-plugin in KB


A webpack plugin allowing to call Flow2 type checker during each webpack compilation.
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Key features

  • It doesn't require flow to be in $PATH.
  • No dependencies. Plugin can reuse project's flow-bin installation.
  • It can make webpack to exit with non-zero return code, if flow validation fails.
  • It works per project, not per file.


Run in you project directory:
npm install --save-dev flow-webpack-plugin flow-bin

or using yarn:
yarn add flow-webpack-plugin flow-bin --dev

Add to your webpack configuration file webpack.config.js:
const FlowWebpackPlugin = require('flow-webpack-plugin')

module.exports = {
    plugins: [
        new FlowWebpackPlugin(),
        // ...
    // ...

Note: flow-bin package is not a hard dependency. If flow is already installed on your system, it can be reused through flowPath option.


Valid codebase:
Valid codebase
Flow validation error:
Flow validation error


Constructor of FlowWebpackPlugin accepts optional configuration object of following properties:
const FlowWebpackPlugin = require('flow-webpack-plugin')

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

| option | type | default value | description | | --- | --- | --- | --- | | failOnError | boolean | false | Webpack exits with non-zero error code if flow typechecking fails. | | failOnErrorWatch | boolean | false | Webpack in watch mode exits with non-zero error code if flow typechecking fails. | | reportingSeverity | 'warning' | 'error' | 'error' | Webpack severity level of reported flow type problems. When using webpack-dev-server, page reload is blocked in case of webpack error. warning can be used to enable page reloads in case of flow errors when using webpack-dev-server. | | printFlowOutput | boolean | true | true ~ Output of flow is printed at the end of webpack compilation in case of error, false ~ output of flow is discarded. | | flowPath | string | require('flow-bin') if flow-bin package is installed. Otherwise the parameter is required. | Path to flow executable. It may be both absolute, relative to the 'cwd' of webpack process or just name of an executable on the PATH. | flowArgs | Array<string> | ['--color=always'] if standard output is directed to a terminal, otherwise [] | Flow command line arguments. See flow cli documentation1. | | verbose | boolean | false | It enables plugin logging for debug purposes. | | callback | ({exitCode: number, stdout: string, stderr: string}) => ?Promise<any> | (result) => {} | Custom user function that is called when Flow check finishes and is passed Flow type check result. If function returns a promise, it is called asynchronously. |

Type annotations strip

This plugin performs type validation of the code. To remove the Flow type annotations and create pure Javascript code babel-plugin-transform-flow-strip-types3 can be used.