Simple gulpfile for building css, js, html and assets with compass, browserify, nunjucks and moving them from app to _build folder

Gulpfile.js

var gulp = require('gulp');
    autoprefixer = require('gulp-autoprefixer'),
    browserify = require('browserify'),
    clean = require('gulp-clean'),
    compass = require('gulp-compass'),
    es = require('event-stream'),
    glob = require('glob'),
    rename = require('gulp-rename'),
    source = require('vinyl-source-stream'),
    nunjucks = require('gulp-nunjucks');

gulp.task( 'compass', function() {
    gulp.src( './app/**/*.scss' )
        .pipe( compass({
            config_file: './config.rb',
            css: './_build',
            sass: './app/'
        }) )
        .pipe( autoprefixer() )
        .pipe( gulp.dest( './build' ) );
});

gulp.task( 'browserify', function( done ) {
    glob('./app/**/*.js', function( err, files ) {
        if ( err ) {
            done( err );
        }

        var tasks = files.map( function( file ) {
            return browserify( { entries: [ file ] } )
                .transform( 'babelify', { presets: [ 'es2015' ] } )
                .bundle()
                .pipe( source( file ) )
                .pipe( rename( function ( path ) {
                    path.dirname = path.dirname.replace( /app\/?/, '' );
                } ) )
                .pipe( gulp.dest( './_build' ) );
            });

        es.merge( tasks ).on( 'end', done );
    });
});

gulp.task( 'nunjucks', function() {
    gulp.src( './app/**/*.html' )
        .pipe( nunjucks.compile() )
        .pipe( gulp.dest( './_build' ) );
});

gulp.task( 'assets-copy', function() {
    gulp.src([
        './app/**/*',
        '!./app/**/*.js',
        '!./app/**/*.scss',
        '!./app/**/*.html'
    ])
    .pipe( gulp.dest( '_build' ) );
});

gulp.task('clean', function() {
    return gulp.src( '_build', { read: false } )
        .pipe( clean() );
});

gulp.task( 'w', [ 'default' ], function() {
    gulp.watch( './app/**/*.html', [ 'nunjucks' ] );
    gulp.watch( './app/**/*.js', [ 'browserify' ]);
    gulp.watch( './app/**/*.scss', [ 'compass' ]);
    gulp.watch([
        './app/**/*',
        '!./app/**/*.js',
        '!./app/**/*.scss',
        '!./app/**/*.html'
    ], [ 'assets-copy' ]);
});

gulp.task( 'default', [ 'clean' ], function() {
    gulp.start( 'compass', 'browserify', 'nunjucks', 'assets-copy' );
});