Example of javascript bundling using Gulp

gulpfile.js

/*jslint node: true */
"use strict";

const $           = require('gulp-load-plugins')();
const argv        = require('yargs').argv;
const gulp	      = require('gulp');
const browserSync = require('browser-sync').create();
const merge       = require('merge-stream');
const colors      = require('colors');
const gutil       = require('gulp-util');
const cleanCSS 	  = require('gulp-clean-css');


const PATHS = {
  sass: [
    'assets/scss/**',
  ],
  javascript: [
    // Include your own custom scripts (located in the custom folder)
    //'bower_components/fastclick/lib/fastclick.js',
    'bower_components/bootstrap-sass/assets/javascripts/bootstrap.js', 
    'assets/js/custom/*.js'
  ]
};

// Combine JavaScript into one file
// In production, the file is minified
gulp.task('javascript', function() {

  return gulp.src(PATHS.javascript)
    .pipe($.sourcemaps.init())
    .pipe($.babel())
    .pipe($.concat('script.js'))
    .pipe($.if(isProduction, uglify ))
    .pipe($.if(!isProduction, $.sourcemaps.write()))
    .pipe(gulp.dest('assets/js'))
    .pipe(browserSync.stream());
    
});