gulpfile.js

var gulp = require('gulp'),
    concat = require('gulp-concat'),
    uglify = require('gulp-uglify'),
    browserify = require('gulp-browserify'),
    sourcemaps = require('gulp-sourcemaps');

var paths = {
    webroot: './wwwroot/'
};
paths.js = paths.webroot + 'js/app/**/*.js';
paths.minJs = paths.webroot + 'js/**/*.min.js';
paths.es5 = paths.webroot + 'js/**/*.es5.js';

gulp.task('build:app', function () {
    return gulp.src([paths.js, '!' + paths.es5, '!' + paths.minJs], {base: '.'})
        .pipe(sourcemaps.init({loadMaps: true}))
        .pipe(concat("bundle.js"))
        .pipe(browserify({
            transform: ['babelify']
        }))
        .pipe(uglify())
        .pipe(sourcemaps.write("."))
        .pipe(gulp.dest(paths.webroot + 'js/'))
        .on('error', console.error);
});

More Info

https://imgur.com/a/hqulpVZ