gulpfile running browserify, babel, and uglify

gulpfile.js

// import libraries installed via NPM
var gulp   = require('gulp'),
    rename = require('gulp-rename'),
    uglify = require('gulp-uglify'),
    notify = require('gulp-notify'),
    browserify = require('browserify'),
    transform = require('vinyl-transform'),
    source = require('vinyl-source-stream'),
    gutil = require( 'gulp-util' ),
    babelify = require( 'babelify' ),
    buffer = require( 'vinyl-buffer' )

// define a task named build that we can run from the command line
// or using gulp
gulp.task('build', function () {
  
  // browserify our data
  browserify()
    // what file is our browserify entry point
    .require( './js/index.js', { entry: true } )
    // convert ES2015 to ES5 via babel
    .transform( babelify, { presets:['es2015'] })
    // create Node.js stream using browserify output
    .bundle()
    // add Vinyl meta-data to Node.js stream, in this case
    // the name of the file we're streaming
    .pipe( source('index.js') )
    // rename stream to bundle.js for output
    .pipe( rename ('bundle.js') )
    // output file to dist folder
    .pipe( gulp.dest('./dist') )
    // collect chunks into a single buffer for
    // buffer-based processing that operates on entire files
    // instead of chunks
    .pipe( buffer() )
    // minimize our bufferr
    .pipe( uglify() )
    // rename our file for output
    .pipe( rename ('bundle.min.js') )
    // send minimized output to dist folder
    .pipe( gulp.dest('./dist') )
    // create notification that build is complete
    .pipe( notify({
      message: 'build complete.',
      onLast:true
    }) )
})

// watch our js folder and trigger build task
// whenever a .js file is changed
gulp.task( 'watch', function() {
  gulp.watch( './js/**.js', function() {
    gulp.run('build')
  })
})

// define default task whenever 'gulp' is run
// in the terminal without explicitly naming another task
gulp.task( 'default', ['build'] )