gulpfile.js

var gulp = require('gulp'),
    plumber = require('gulp-plumber'),
    sass = require('gulp-sass'),
    gutil = require('gulp-util'),
    notify = require('gulp-notify'),
    browserSync = require('browser-sync');

gulp.task('sass', function () {
    gulp.src('scss/app.scss')
        .pipe(plumber())
        .pipe(sass({includePaths: ['scss']}))
        .pipe(notify({ message: 'Sass compiled.' }))
        .pipe(gulp.dest('stylesheets'));
})

gulp.task('browser-sync', function() {
    browserSync.init(["stylesheets/*.css", "js/*.js", "**/*.html"], {
        server: {
            baseDir: "./"
        }
    });
});

gulp.task('default', ['sass', 'browser-sync'], function () {
    gulp.watch("scss/**/*.scss", ['sass'])
        .on('error', gutil.log);
});