BrowserSync + Gulp.js: Simple webServer + liveReload + watching CSS, HTML and SASS files

gulpfile.js

/**
 * This example:
 *  Uses the built-in BrowserSync server for HTML files
 *  Watches & compiles SASS files
 *  Watches & injects CSS files
 * 
 * More details: http://www.browsersync.io/docs/gulp/
 * 
 * Install:
 * npm install browser-sync gulp gulp-sass --save-dev
 * 
 * Then run it with:
 * gulp
 */
var browserSync = require('browser-sync');
var reload      = browserSync.reload;
var gulp        = require('gulp');
var sass        = require('gulp-sass');

// Browser-sync task, only cares about compiled CSS
gulp.task('browser-sync', function() {
    browserSync({
        server: {
            baseDir: "./"
        }
    });
});


// Sass task, will run when any SCSS files change & BrowserSync
// will auto-update browsers
gulp.task('sass', function () {
    return gulp.src('scss/**/*.scss')
        .pipe(sass())
        .pipe(gulp.dest('css'))
        .pipe(reload({stream:true}));
});

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

// Default task to be run with `gulp`
// This default task will run BrowserSync & then use Gulp to watch files.
// When a file is changed, an event is emitted to BrowserSync with the filepath.
gulp.task('default', ['browser-sync'], function () {
    gulp.watch('css/*.css', function (file) {
        if (file.type === "changed") {
            reload(file.path);
        }
    });
    gulp.watch("*.html", ['bs-reload']);
});

you should use arrow functions and const

this should be updated for gulp 4

gulp.task('default', gulp.series('browser-sync', function() {
gulp.watch('css/.css', function (file) {
if (file.type === "changed") {
reload(file.path);
}
});
gulp.watch(".html", ['bs-reload']);
}));