index.js

// add this please
// add this please
require("preact-cli/lib/lib/webpack/polyfills");
// look above

import { h } from "preact";
import habitat from "preact-habitat";

import Widget from "./components/hello-world";

let _habitat = habitat(Widget);

_habitat.render({
  selector: '[data-widget-host="habitat"]',
  clean: true
});

preact.config.js

import path from "path";

export default (config, env, helpers) => {
  // delete config.entry.polyfills;

  let { plugin } = helpers.getPluginsByName(config, "ExtractTextPlugin")[0];
  plugin.options.disable = true;

  if (env.production) {
    config.output.libraryTarget = "umd";
  }
};