ES6 Gulpfile Example

gulpfile.babel.js

/* 
 *    Steps
 * 1. Rename your gulpfile.js to gulpfile.babel.js
 * 2. Add babel to your package.json (npm install -D babel)
 * 3. Start writing ES6 in your gulpfile!
 */
 
 import gulp from 'gulp'; // ES6 imports!
 import sass from 'gulp-sass';
 
 const sassOpts = { outputStyle: 'compressed', errLogToConsole: true }; // "let" and "const"!!
 
 gulp.task('sass', () = > { // Arrow functions!!
   gulp.src('./**/*.scss')
    .pipe(sass(sassOpts))
    .pipe(gulp.dest('./'));
 });
 
 gulp.task('default', ['sass'], () => { // Arrow functions!!
   gulp.watch('./src/sass/**/*.scss', ['sass'])
    .on('change', (e) => {  // Arrow functions!!
      console.log(`File ${e.path} was ${e.type}, running Sass task...`); // Template strings and interpolation!!
    });
 });

The file naming issue is mentioned in Gulp's README:

Node already supports a lot of ES2015+ features, but to avoid compatibility problems we suggest to install Babel and rename your gulpfile.js to gulpfile.babel.js.

The rename worked for me.