See [budiadiono/gulpfile.js](https://gist.github.com/budiadiono/dd409e2168c801c9e7429766ee0101c30)

gulpfile.js

var browserSync = require('browser-sync').create()
var reload = browserSync.reload
var gulp = require('gulp')
var gitbook = require('gitbook')
var path = require('path')
var del = require('del')


// path of your *.md book files
var rootPath = path.join('/gitbook')

// output path where generated *.html will be stored
var outputPath = path.join(rootPath, '_book')

// gulp.watch instance
var watcher


// rebuild book + start server
gulp.task('default', function (done) {
  rebuildBook(function () {
    browserSync.init({
      server: {
        baseDir: outputPath
      },
      port: 40001
    })
    done()
  })
})


// kill watcher + remove/clean output dir + build book
function rebuildBook (done) {

  // pause watcher while building book progress
  if (watcher) {
    watcher.end()
    watcher = undefined;
  }

  // ensure output path is not exists otherwise book won't generated
  return del(path.join(outputPath)).then(paths => {
    buildBook().then(function () {
      
      // start watcher after built
      startWatch().on('ready', function(){        
        done();
      }).on('error', function(e){
        console.error('ERROR: watch error... $s', e)
      })
    })
  })
}


// build book
function buildBook () {
  var fs = gitbook.createNodeFS(rootPath)
  var book = gitbook.Book.createForFS(fs)
  var Parse = gitbook.Parse
  var Output = gitbook.Output
  var Generator = Output.getGenerator('website')

  return Parse.parseBook(book)
    .then(function (resultBook) {
      return Output.generate(Generator, resultBook, {
        root: outputPath
      })
    })
}


// start watching md files + when files changed reload browser
function startWatch() {
  var rp = path.join(rootPath, '/**/*.md')
  watcher = gulp.watch([rp, '!' + rp + '/_book/' ], function () {
    rebuildBook(reload)
  })
  return watcher;
}