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Webpack loader for Fable (F# to JS compiler)


npm install --save-dev webpack babel-core fable-loader


Create a webpack-config.js like the following:

var path = require("path");
var fableUtils = require("fable-utils");
function resolve(relativePath) {
    return path.join(__dirname, relativePath);
var babelOptions = fableUtils.resolveBabelOptions({
  "presets": [
    ["env", {"modules": false}]
module.exports = {
  entry: resolve('src/MyProject.fsproj'),
  output: {
    filename: 'bundle.js',
    path: resolve('build/'),
  resolve: {
    modules: [resolve("node_modules/")]
  module: {
    rules: [
        test: /\.fs(proj|x)?$/,
        use: {
          loader: "fable-loader",
          options: {
            define: ["DEBUG"],
            babel: babelOptions
        test: /\.js$/,
        exclude: /node_modules/,
        use: {
          loader: 'babel-loader',
          options: babelOptions

Note we're resolving paths as well as Babel options and node modules to prevent conflicts in case Fable pulls files from outside the project local directory (for example, from Nuget cache).

Add this to your package.json.

  "build": "webpack"

You can then bundle your app by running: dotnet fable npm-run build.

Check Fable website for more info

As you can see in the sample, normally you'll install babel-loader for other JavaScript files in your project (including those in Fable.Core) and you'll share the Babel options between both loaders. Check Babel website to find more info about the available options.

These are the options that can be passed to fable-loader:

  • babel: Babel options as mentioned above.
  • define: Array of compiler directives passed to the F# compiler (like DEBUG). Note Fable will ignore the DefineConstants property in .fsproj.
  • plugins: Array of paths to Fable plugins (.dll files).
  • typedArrays: Translate numeric arrays as JS Typed Arrays. True by default.
  • clampByteArrays: If true, Fable will translate byte arrays as Uint8ClampedArray.
  • fableCore: Specify a directory containing Fable.Core JS files, normally used for testing new Fable versions.