How to use the @angular/service-worker/config.Generator function in @angular/service-worker

export function augmentAppWithServiceWorker(projectRoot: string, appRoot: string,
    outputPath: string, baseHref: string): Promise {
  // Path to the worker script itself.
  const workerPath = resolveProjectModule(projectRoot, '@angular/service-worker/ngsw-worker.js');
  const safetyPath = path.join(path.dirname(workerPath), 'safety-worker.js');
  const configPath = path.resolve(appRoot, 'ngsw-config.json');

  if (!fs.existsSync(configPath)) {
    throw new Error(oneLine`Error: Expected to find an ngsw-config.json configuration
      file in the ${appRoot} folder. Either provide one or disable Service Worker
      in .angular-cli.json.`);
  }
  const config = fs.readFileSync(configPath, 'utf8');

  const Generator = require('@angular/service-worker/config').Generator;
  const gen = new Generator(new CliFilesystem(outputPath), baseHref);
  return gen
    .process(JSON.parse(config))
    .then((output: Object) => {
      const manifest = JSON.stringify(output, null, 2);
      fs.writeFileSync(path.resolve(outputPath, 'ngsw.json'), manifest);
      // Copy worker script to dist directory.
      const workerCode = fs.readFileSync(workerPath);
      fs.writeFileSync(path.resolve(outputPath, 'ngsw-worker.js'), workerCode);

      // If @angular/service-worker has the safety script, copy it into two locations.
      if (fs.existsSync(safetyPath)) {
        const safetyCode = fs.readFileSync(safetyPath);
        fs.writeFileSync(path.resolve(outputPath, 'worker-basic.min.js'), safetyCode);
        fs.writeFileSync(path.resolve(outputPath, 'safety-worker.js'), safetyCode);
      }
    });

function augmentAppWithServiceWorker(projectRoot, appRoot, outputPath, baseHref) {
    // Path to the worker script itself.
    const workerPath = require_project_module_1.resolveProjectModule(projectRoot, '@angular/service-worker/ngsw-worker.js');
    const safetyPath = path.join(path.dirname(workerPath), 'safety-worker.js');
    const configPath = path.resolve(appRoot, 'ngsw-config.json');
    if (!fs.existsSync(configPath)) {
        throw new Error(common_tags_1.oneLine `Error: Expected to find an ngsw-config.json configuration
      file in the ${appRoot} folder. Either provide one or disable Service Worker
      in .angular-cli.json.`);
    }
    const config = fs.readFileSync(configPath, 'utf8');
    const Generator = require('@angular/service-worker/config').Generator;
    const gen = new Generator(new CliFilesystem(outputPath), baseHref);
    return gen
        .process(JSON.parse(config))
        .then((output) => {
        const manifest = JSON.stringify(output, null, 2);
        fs.writeFileSync(path.resolve(outputPath, 'ngsw.json'), manifest);
        // Copy worker script to dist directory.
        const workerCode = fs.readFileSync(workerPath);
        fs.writeFileSync(path.resolve(outputPath, 'ngsw-worker.js'), workerCode);
        // If @angular/service-worker has the safety script, copy it into two locations.
        if (fs.existsSync(safetyPath)) {
            const safetyCode = fs.readFileSync(safetyPath);
            fs.writeFileSync(path.resolve(outputPath, 'worker-basic.min.js'), safetyCode);
            fs.writeFileSync(path.resolve(outputPath, 'safety-worker.js'), safetyCode);
        }
    });
}