Gulp workflow with sass compile, js minification and postcss processing.

gulpfile.js

/* gulp dependencies */
const gulp = require('gulp');  
const sass = require('gulp-sass');
const uglify = require('gulp-uglify');
const rename = require('gulp-rename');
const notify = require('gulp-notify');
const minifycss = require('gulp-minify-css');
const concat = require('gulp-concat');
const plumber = require('gulp-plumber');
const browserSync = require('browser-sync');
const postcss = require('gulp-postcss');
const autoprefixer = require('autoprefixer');
const cssnano = require('cssnano');
const reload = browserSync.reload;

/* scripts task */
gulp.task('scripts', function() {
	return gulp.src([
		'node_modules/jquery/dist/jquery.js',
		'src/js/main.js'
	])
	.pipe(concat('main.js'))
	.pipe(gulp.dest('assets/js'))
	.pipe(rename({suffix: '.min'}))
	.pipe(uglify())
	.pipe(gulp.dest('assets/js'));
});

/* sass task */
gulp.task('sass', function() {  
	gulp.src('src/scss/main.scss')
		.pipe(plumber())
		.pipe(sass({
			includePaths: ['scss']
		}))
		.pipe(gulp.dest('assets/css'));
});

/* postcss/cssnano task */
gulp.task('css', function() {
    var processors = [
        autoprefixer({browsers: ['last 4 versions']}),
        cssnano(),
    ];
    return gulp.src('assets/css/main.css')
        .pipe(postcss(processors))
        .pipe(rename({suffix: '.min'}))
        .pipe(gulp.dest('assets/css'))
        .pipe(reload({stream: true}));
});

/* reload task */
gulp.task('bs-reload', function() {
	browserSync.reload();
});

/* browser-sync for localhost */
gulp.task('browser-sync', function() {
	browserSync.init(['assets/css/*.css', 'assets/js/*.js'], {
		proxy: 'website.dev'
	});
});

/* watch scss, js and html files, doing different things with each. */
gulp.task('default', ['sass', 'css', 'browser-sync'], function() {
	/* watch scss, run the sass task on change. */
	gulp.watch(['src/scss/*.scss', 'src/scss/**/*.scss'], ['sass', 'css']);
	/* watch app.js file, run the scripts task on change. */
	gulp.watch(['src/js/main.js'], ['scripts']);
	/* watch .html files, run the bs-reload task on change. */
	gulp.watch(['*.html'], ['bs-reload']);
});

package.json

  "name": "package-name",
  "version": "1.0.0",
  "description": "",
  "main": "index.html",
  "dependencies": {},
  "devDependencies": {
    "autoprefixer": "^6.5.3",
    "browser-sync": "^2.17.5",
    "cssnano": "^3.8.0",
    "gulp": "^3.9.1",
    "gulp-concat": "^2.6.0",
    "gulp-minify-css": "^1.2.4",
    "gulp-notify": "^2.2.0",
    "gulp-plumber": "^1.1.0",
    "gulp-postcss": "^6.2.0",
    "gulp-rename": "^1.2.2",
    "gulp-sass": "^2.3.2",
    "gulp-uglify": "^2.0.0",
    "gulp-util": "^3.0.7",
    "jquery": "2.2.4"
  },
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Shealan Forshaw",
  "license": "ISC"
}