gulpfile.js

var gulp = require('gulp');
var watch = require('gulp-watch');
var del = require('del');
var uglify = require('gulp-uglify');
var notify = require('gulp-notify');
var rename = require('gulp-rename');
var concat = require('gulp-concat');
var browserify = require('gulp-browserify');
/**
CSS related
*/
var less = require('gulp-less');
var minifyCSS = require('gulp-minify-css');
var concatCss = require('gulp-concat-css');

/**
Images processing
*/
var imagemin = require('gulp-imagemin');
/**
  Call this task indepedently Using 'gulp js'
**/
gulp.task('js', function() {
  gulp.watch('./src/assets/js/*.js', ['js']);
  return gulp.src('./src/assets/js/*.js')
    .pipe(browserify({
      insertGlobals: true,
      debug: !gulp.env.production,
    }))
    .pipe(concat('build.js'))
    .pipe(rename({ suffix: '.min' }))
    .pipe(uglify())
    .pipe(gulp.dest('./dist/assets/js'))
    .pipe(notify({ message: 'scripts task finished!' }));
});

gulp.task('less', function() {
  gulp.watch('./src/assets/less/*.less', ['less']);
  return gulp.src('./src/assets/less/*.less')
      .pipe(less())
      .pipe(concatCss('bundle.css')) // name of concated css.
      .pipe(minifyCSS())
      .pipe(gulp.dest('./dist/assets/css'));
});

gulp.task('image', function() {
  return gulp.src('./src/assets/img/*')
    .pipe(imagemin({ optimizationLevel: 3, progressive: true, interlaced: true }))
    .pipe(gulp.dest('./dist/assets/img'))
    .pipe(notify({ message: 'images compression finished!' }));
});

gulp.task('clean', function(cb) {
  del(['./dist/assets'], cb);
});

/**
  default task by 'gulp' and do js task
**/
gulp.task('default', ['js', 'less', 'image']);