How to use selenium-standalone

gulp.task('selenium', function (done) {
 selenium.install({
  logger: function (message) { console.log(message)}
 }, function (err) {
  if (err) return done(err);

  selenium.start(function (err, child) {
   if (err) return done(err);
   selenium.child = child;
   done();
  });
 });
});

function startSelenium(callback) {
 // Start selenium
 var opts = {version: '2.42.0'};
 selenium.install(opts, function(err) {
  if (err) {
   console.error('Failed to install selenium');
   process.exit(1);
  }
  selenium.start(opts, function(err, server) {
   sauceClient = wd.promiseChainRemote();
   callback();
  });
 });
}

gulp.task('e2e', ['test', 'selenium'], function () {
  return gulp.src('wdio.conf.js', {read: false})
    .pipe(webdriver({
      // this is here because gulp-webdriver doesn't deal with a project with a flattened dependency (at the top level) on webdriverio
      // see https://github.com/webdriverio/gulp-webdriver/issues/20
      wdioBin: path.join(__dirname, 'node_modules', '.bin', 'wdio'),
      desiredCapabilities: {
        browserName: 'phantomjs'
      }
    }))
    .once('end', function () {
      selenium.child.kill();
    });

});