Flow Babel Webpack Plugin

A concise tool that glues together Flow and Webpack, with the help of Babel.

It provides you with flow typecheck status in webpack build reports.

Usage

Since JS and Flow syntax vary slightly, you will need to get rid of the type annotations.

This is where transform-flow-comments comes in. It converts flow type annotations into comments that Flow understands.

You need to follow a few simple steps.

1. Install dependencies

# Install Babel and Webpack and save as devDependencies
npm i -D babel-core babel-loader webpack

# Install FBWP
npm i -D flow-babel-webpack-plugin

2. Setup babel and flow

# setup .flowconfig
./node_modules/.bin/flow init

# or if you have global `flow`
flow init

# .babelrc file
{
  "plugins" : [
    "transform-flow-comments"
  ]
}

3. Setup webpack config

// webpack.config.js file

var FlowBabelWebpackPlugin = require('flow-babel-webpack-plugin');

module.exports = {
  entry: './index',

  output: {
    filename: 'build.js',
  },

  module: {
    loaders: [
      {
        test: /\.js$/,
        loader: 'babel',
      },
    ],
  },

  plugins: [
    new FlowBabelWebpackPlugin(),
  ],
}

And that's it!

From now on, when you run webpack, you will recieve flow status reports alongside your webpack build log.

Something like this.

Options

It should work pretty well with the defaults, but there are some options available:

warn

If you'd prefer to treat Flow issues as webpack warnings instead of errors, you can enable this option.

plugins: [
  new FlowBabelWebpackPlugin({
    warn: true,
  }),
],

formatter

You can provide your own error message formatting function in order to customize the output.

For example:

plugins: [
  new FlowBabelWebpackPlugin({
    formatter: function (errorCode, errorDetails) {
      return 'A Flow error was detected: ' + errorCode + '\n\n' + errorDetails;
    },
  }),
],

What's next?

Nothing much, really. All I wanted was to display flow reports alongside webpack's - nothing fance.

I might add something more to it, if I find it really useful. Some options are:

• IO redirection for further logging or processing
• External file checks, i.e., files that lie outside of project's root folder

If you have something in mind, or something you want, feel free to ask.