FlowgenWebpackPlugin.js

// Generate .flow.js from .ts files so that flow can understand TS and the two can live in peace at least until we have time to completely overhaul flow
const flowgen = require('flowgen');
const fs = require('fs');
const name = 'FlowgenWebpackPlugin';
const tsPattern = /\.(ts|tsx)$/;
class FlowgenWebpackPlugin {
  apply(compiler) {
    compiler.hooks.compilation.tap(name, compilation => {
      const compiledModules = {};
      compilation.hooks.succeedModule.tap(name, module => {
        if (
          module.issuer &&
          tsPattern.test(module.issuer.resource) &&
          !compiledModules[module.issuer.resource]
        ) {
          fs.writeFile(
            `${module.issuer.resource}.flow`,
            flowgen.beautify(
              flowgen.compiler.compileDefinitionFile(module.issuer.resource)
            )
          );
          compiledModules[module.issuer.resource] = true;
        }
      });
    });
  }
}

module.exports = FlowgenWebpackPlugin;