gulpfile.js

/*
  This is an EXAMPLE gulpfile.js
  You'll want to change it to match your project.
  Find plugins at https://npmjs.org/browse/keyword/gulpplugin
*/
var gulp = require('gulp');
var uglify = require('gulp-uglify');

gulp.task('scripts', function() {
  // Minify and copy all JavaScript (except vendor scripts)
  gulp.src(['client/js/**/*.js', '!client/js/vendor/**'])
    .pipe(uglify())
    .pipe(gulp.dest('build/js'));

  // Copy vendor files
  gulp.src('client/js/vendor/**')
    .pipe(gulp.dest('build/js/vendor'));
});

// Copy all static assets
gulp.task('copy', function() {
  gulp.src('client/img/**')
    .pipe(gulp.dest('build/img'));

  gulp.src('client/css/**')
    .pipe(gulp.dest('build/css'));

  gulp.src('client/*.html')
    .pipe(gulp.dest('build'));
});

// The default task (called when you run `gulp`)
gulp.task('default', function() {
  gulp.run('scripts', 'copy');

  // Watch files and run tasks if they change
  gulp.watch('client/js/**', function(event) {
    gulp.run('scripts');
  });

  gulp.watch([
    'client/img/**',
    'client/css/**',
    'client/*.html'
  ], function(event) {
    gulp.run('copy');
  });
});

taskFile.js

var uglifyJS = require('uglify-js');
var glob = require('glob-stream').create;
var watch = require('glob-watcher');
var through = require('through');
var fs = require('fs');
var path = require('path');

// uglify -.- wtf. make stream kind of.
// gulp-uglify should be like this instead!
function uglify() {
  var stream = through()

  // mikeal style pipe hack because uglify -.-
  stream.on('pipe', function (src) {
    var fileName = src.fileName
    fs.readFile(fileName, function (err, file) {
      if (err) {
        return stream.emit('error', err)
      }

      var payload

      try {
        payload = uglifyJS.minify(String(file), { fromString: true }).code
      } catch (err) {
        return stream.emit('error', err)
      }

      stream.end(payload)
    })
  })

  return stream
}

// gulp.src should be like this!
function src(patterns) {
  return glob(patterns)
    .pipe(through(function (file) {
      var stream = fs.createReadStream(file.path)
      stream.fileName = file.path
      return stream
    }))
}

// gulp.dest should be like this!
function dest(baseDir) {
  return through(function (fileStream) {
    fileStream.pipe(fs.createWriteStream(
      path.join(baseDir, path.filename(fileStream.fileName))
    ))
  })
}

// gulp.task is not needed, just use functions!
var tasks = {
  'scripts': function () {
    src(['client/js/**/*.js', '!client/js/vendor/**'])
      .pipe(through(function (fileStream) {
        return fileStream.pipe(uglify());
      }))
      .pipe(dest('build/js'))

    src('client/js/vendor/**')
      .pipe(dest('build/js/vendor'))
  },
  'copy': function () {
    src('client/img/**')
      .pipe(dest('build/img'))

    src('client/css/**')
      .pipe(dest('build/css'))

    src('client/*.html')
      .pipe(dest('build'))
  },
  'default': function () {
    tasks.scripts()
    tasks.copy()

    watch('client/js/**', tasks.scripts)

    watch([
      'client/img/**',
      'client/css/**',
      'client/*.html'
    ], tasks.copy)
  }
}

// you don't need a special gulp command
// just node taskFile.js scripts to run scripts.
// or `alias gulp = node taskFile.js`
var cmd = process.argv[3] || 'default';
tasks[cmd]();