gulpfile.js

var gulp        = require('gulp');
var jshint      = require('gulp-jshint');
var uglify      = require('gulp-uglify');
var concat      = require('gulp-concat');
var less        = require('gulp-less');
var minifyCSS   = require('gulp-minify-css');
var prefix      = require('gulp-autoprefixer');

var del         = require('del');
var bSync       = require('browser-sync');

gulp.task('test', function() {
   return gulp.src(['app/scripts/**/*.js', '!app/scripts/vendor/**/*.js'])
    .pipe(jshint())
    .pipe(jshint.reporter('default'))
    .pipe(jshint.reporter('fail'));
});


gulp.task('scripts',
   gulp.series('test', function scriptsInternal() {
     return gulp.src(['app/scripts/**/*.js', '!app/scripts/vendor/**/*.js'])
       .pipe(concat('main.min.js'))
       .pipe(uglify())
       .pipe(gulp.dest('dist/scripts'));
   })
);

gulp.task('styles', function() {
  return gulp.src('app/styles/main.less')
    .pipe(less())
    .pipe(minifyCSS())
    .pipe(prefix())
    .pipe(gulp.dest('dist/styles'));
});

gulp.task('clean', function(done) {
  return del(['dist']);
});

gulp.task('server', function(done) {
  bSync({
    server: {
      baseDir: ['dist', 'app']
    }
  })
  done();
})

gulp.task('default', gulp.series('clean', gulp.parallel('styles', 'scripts'), 'server',
  function watcher(done) {
    gulp.watch(['app/scripts/**/*.js', '!app/scripts/vendor/**/*.js'], gulp.parallel('scripts'));
    gulp.watch('app/styles/**/*.less', gulp.parallel('styles'));
    gulp.watch('dist/**/*', bSync.reload);
  })
);