Example gulpfile

gulpfile.js

// including plugins
var gulp = require('gulp');
var browserSync = require('browser-sync');
var minifyHtml = require('gulp-minify-html');
var minifyCss = require('gulp-minify-css');
var uglify = require('gulp-uglify');
var runSequence = require('run-sequence');
var clean = require('gulp-clean');
var injectPartials = require('gulp-inject-partials');
var imagemin = require('gulp-imagemin');

var sitemap = require('gulp-sitemap');

var folder = './_site/';
var siteUrl = 'https://31apps.com/';

// npm init
// npm install gulp browser-sync gulp-minify-html gulp-minify-css gulp-uglify run-sequence gulp-clean gulp-inject-partials gulp-sitemap gulp-imagemin --save

// https://julienrenaux.fr/2014/05/25/introduction-to-gulp-js-with-practical-examples/

gulp.task('default', ['maintask'], function (callback) {
	//runs maintask first, then:
	return runSequence('serve', 'watch', callback);
});

gulp.task('maintask', function(callback) {
	// it runs 'clean' then 'copyall' then the other ones in parallel then callback
	return runSequence(
		'clean',
		'copyall',
		'sitemap',
		['minify-html', 'minify-css', 'minify-js', 'minify-imgs'],
		callback);
});

gulp.task('watch',function() {
	return gulp.watch(folder + '**/*', ['maintask', browserSync.reload]);
});

gulp.task('serve', function() {
	return browserSync({
		server: {
			baseDir: 'dist'
		},
		port: 3010
	});
});

gulp.task('clean', function () {
    return gulp.src('./dist/', {read: false})
        .pipe(clean());
});

gulp.task('copyall', function () {
	return gulp.src([folder + '**/*', folder + '*', folder + '.*'])
		.pipe(gulp.dest('./dist/'));
});

gulp.task('minify-html', function () {
    return gulp.src(folder + '**/*.html')
		.pipe(injectPartials())
		.pipe(minifyHtml())
	    .pipe(gulp.dest('./dist/'));
});

gulp.task('minify-css', function () {
    return gulp.src(folder + '**/*.css')
	    .pipe(minifyCss())
	    .pipe(gulp.dest('./dist/'));
});

gulp.task('minify-js', function () {
    return gulp.src(folder + '**/*.js')
	    .pipe(uglify())
	    .pipe(gulp.dest('./dist/'));
});

gulp.task('minify-imgs', function () {
	return gulp.src(folder + '**/*.{png,jpg,gif,svg,jpeg}')
		.pipe(imagemin())
		.pipe(gulp.dest('./dist/'));
});

gulp.task('sitemap', function () {
	gulp.src('dist/**/*.html', {
		read: false
	})
	.pipe(sitemap({
		siteUrl: siteUrl
	}))
	.pipe(gulp.dest('./dist/'));
});

package.json

{
	"devDependencies": {
		"browser-sync": "^2.18.8",
		"gulp": "^3.9.1",
		"gulp-clean": "^0.3.2",
		"gulp-imagemin": "^3.1.1",
		"gulp-inject-partials": "^1.0.2",
		"gulp-minify-css": "^1.2.4",
		"gulp-minify-html": "^1.0.6",
		"gulp-uglify": "^2.0.1",
		"run-sequence": "^1.2.2",
		"sw-precache": "^5.0.0"
	}
}