How to use the @now/build-utils.createLambda function in @now/build-utils

debug('Running `go build`...');
    const destPath = join(outDir, 'handler');
    try {
      const src = [
        join(entrypointDirname, mainGoFileName),
        downloadedFiles[entrypoint].fsPath,
      ];
      await go.build(src, destPath);
    } catch (err) {
      console.log('failed to `go build`');
      throw err;
    }
  }

  const lambda = await createLambda({
    files: { ...(await glob('**', outDir)), ...includedFiles },
    handler: 'handler',
    runtime: 'go1.x',
    environment: {},
  });

  const watch = parsedAnalyzed.watch;
  let watchSub: string[] = [];
  // if `entrypoint` located in subdirectory
  // we will need to concat it with return watch array
  if (entrypointArr.length > 1) {
    entrypointArr.pop();
    watchSub = parsedAnalyzed.watch.map(file => join(...entrypointArr, file));
  }

  return {

...nodeModules
  }

  // Extra files to be included in lambda
  const serverFiles = [
    ...(Array.isArray(config.serverFiles) ? config.serverFiles : []),
    'package.json'
  ]

  for (const pattern of serverFiles) {
    const files = await glob(pattern, rootDir)
    Object.assign(launcherFiles, files)
  }

  // lambdaName will be titled index, unless specified in nuxt.config.js
  lambdas[lambdaName] = await createLambda({
    handler: 'now__launcher.launcher',
    runtime: meta.isDev ? 'nodejs' : nodeVersion.runtime,
    files: launcherFiles,
    environment: {
      NODE_ENV: 'production'
    }
  })

  // await download(launcherFiles, rootDir)

  endStep()

  return {
    output: {
      ...lambdas,
      ...clientDistFiles,

if (shouldAddSourcemapSupport) {
    launcherFiles[`${SOURCEMAP_SUPPORT_FILENAME}.js`] = new FileFsRef({
      fsPath: join(__dirname, 'source-map-support.js'),
    });
  }

  if (shouldAddHelpers) {
    launcherFiles[`${HELPERS_FILENAME}.js`] = new FileFsRef({
      fsPath: join(__dirname, 'helpers.js'),
    });
  }

  // Use the system-installed version of `node` when running via `now dev`
  const runtime = meta.isDev ? 'nodejs' : nodeVersion.runtime;

  const lambda = await createLambda({
    files: {
      ...preparedFiles,
      ...launcherFiles,
    },
    handler: `${LAUNCHER_FILENAME}.launcher`,
    runtime,
  });

  return { output: lambda, watch };
}

}
        console.log("Mountpoint is: " + JSON.stringify(mountpoint));
        console.log("Routes are: " + JSON.stringify(routes));
        validateDistDir(distPath, meta.isDev, config);
        const statics = await build_utils_1.glob("**", distPath, mountpoint);
        console.log("Output files are: " + JSON.stringify(statics));
        console.log("Server.js is: " + JSON.stringify(statics["server.js"]));
        const launcherFiles = {
            "now__bridge.js": new build_utils_1.FileFsRef({
                fsPath: require("@now/node-bridge")
            }),
            "now__launcher.js": new build_utils_1.FileFsRef({
                fsPath: path_1.default.join(__dirname, "launcher.js")
            })
        };
        const lambda = await build_utils_1.createLambda({
            runtime: "nodejs8.10",
            handler: "now__launcher.launcher",
            files: {
                ...launcherFiles,
                "index.js": new build_utils_1.FileFsRef({
                    fsPath: statics["server.js"].fsPath
                })
            }
        });
        const output = {
            ...statics,
            "main.js": lambda
        };
        console.log("Finished!");
        return { routes, output };
    }

validateDistDir(distPath, meta.isDev, config);
    const statics = await glob("static/**", distPath);
    const server = await glob("server.js", distPath);
    const favicon = await glob("favicon.ico", workPath);

    const launcherFiles = {
      "now__bridge.js": new FileFsRef({
        fsPath: require("@now/node-bridge")
      }),
      "now__launcher.js": new FileFsRef({
        fsPath: path.join(__dirname, "launcher.js")
      })
    };

    const lambda = await createLambda({
      runtime: "nodejs12.x",
      handler: "now__launcher.launcher",
      files: {
        ...launcherFiles,
        "index.js": new FileFsRef({
          fsPath: server["server.js"].fsPath
        })
      }
    });

    const output = {
      ...statics,
      ...favicon,
      "server.js": lambda
    };