webpack.flow-plugin.js

const execFile = require('child_process').execFile;
const flow = require('flow-bin');

function FlowPlugin(options) {

}

FlowPlugin.prototype.apply = function(compiler) {
  var errors = [];

  function flowCheck() {
    var cb = arguments[arguments.length - 1];
    execFile(flow, ['check'], (err, result) => {
      if (err !== null) {
        errors.push(new Error(result));
      }

      cb();
    });
  }

  compiler.plugin("run", flowCheck);
  compiler.plugin("watch-run", flowCheck);

  compiler.plugin("compilation", function(compilation) {
    errors.forEach((error) => compilation.errors.push(error));
    errors = [];
  });
};

module.exports = FlowPlugin;