gulpfile.js

/*eslint-env-node*/

var gulp = require('gulp'),
    sass = require('gulp-sass'),
    autoprefixer = require('gulp-autoprefixer'),
    concat = require('gulp-concat'),
    uglify = require('gulp-uglify'),
    babel = require('gulp-babel'),
    sourcemaps = require('gulp-sourcemaps');

gulp.task('default', ['scripts', 'styles'], () => {
  gulp.watch('sass/**/*.scss', ['styles']);
  gulp.watch('js/**/*.js', ['scripts']);
});

gulp.task('styles', () => {
  gulp.src('sass/**/*.scss')
      .pipe(sourcemaps.init())
      .pipe(sass({
        outputStyle: 'compressed'
      })
      .on('error', sass.logError))
      .pipe(autoprefixer({
        browsers: ['last 2 versions']
      }))
      .pipe(sourcemaps.write())
      .pipe(gulp.dest('./css'));
});

gulp.task('scripts', () => {
  gulp.src('js/**/*.js')
      .pipe(sourcemaps.init())
      .pipe(babel({
        presets: ['env']
      }))
      .pipe(concat('all.js'))
      .pipe(uglify())
      .pipe(sourcemaps.write())
      .pipe(gulp.dest('./js'));
});