My personal gist

gulpfile.js

const gulp = require("gulp");
const sass = require("gulp-sass");
const concat = require("gulp-concat");
const cssnano = require("gulp-cssnano");
const uglify = require("gulp-uglify");
const prefix = require("gulp-autoprefixer");
let autoPrefixer = [
  "> 1%",
  "last 2 versions",
  "firefox >= 4",
  "safari 7",
  "safari 8",
  "IE 8",
  "IE 9",
  "IE 10",
  "IE 11"
];
gulp.task("default", ["watch"]);

gulp.task("watch", ["sass", "scripts"], function() {
  gulp.watch("public/sass/**/*.scss", ["sass"]);
  gulp.watch("public/js/main.js", ["scripts"]);
});

gulp.task("sass", function() {
  return gulp
    .src("public/sass/**/*.scss")
    .pipe(sass())
    .pipe(cssnano())
    .pipe(prefix({ browsers: autoPrefixer }))
    .pipe(concat("styles.min.css"))
    .pipe(gulp.dest("public/css"));
});

gulp.task("scripts", function() {
  return gulp
    .src("public/js/main.js")
    .pipe(concat("main.min.js"))
    .pipe(uglify())
    .pipe(gulp.dest("public/js"));
});