gulpfile.js

// -------------------- Required modules --------------------
var { task, src, dest, watch, series, parallel } = require('gulp'),
	concat = require('gulp-concat'),
	chmod = require('gulp-chmod'),
	plumber = require('gulp-plumber'),
	postcss = require('gulp-postcss'),
	sass = require('gulp-sass'),
	autoprefixer = require('autoprefixer'),
	cssnano = require('cssnano'),
	removeSourcemaps = require('gulp-remove-sourcemaps');

sass.compiler = require('node-sass');

// -------------------- Configure object --------------------
var config = {};
config.src = './src';
config.JS = config.src + '/js';
config.SCSS = config.src + '/scss';
config.CSS = config.src + '/css';
config.buildTasks = ['sass', 'js'];
config.jsFiles = ['node_modules/jquery/dist/jquery.min.js', 'node_modules/popper.js/dist/umd/popper.min.js', 'node_modules/bootstrap/dist/js/bootstrap.min.js'];

//  -------------------- Gulp Tasks --------------------
// Compile SASS into CSS
task('sass', function() {
	var plugins = [
		autoprefixer(),
		cssnano()
	];
	return src(config.SCSS +'/*.scss')
		.pipe(plumber())
		.pipe(sass())
		.pipe(postcss(plugins))
		.pipe(chmod(0o755))
		.pipe(dest(config.CSS))
});

// Move the JS files into our /src/js folder
task('js', function() {
	return src(config.jsFiles)
		.pipe(plumber())
		.pipe(removeSourcemaps())
		.pipe(concat('vendor.js'))
		.pipe(dest(config.JS))
});

// Watches scss files
task('watch', series('sass', function(done) {
	watch([config.SCSS + '/*.scss', config.SCSS + '/_*.scss'], series('sass'));
	done();
}));

task('build', series(config.buildTasks));

task('default', series('watch'));