Попробуйте так, должно помочь:
const
gulp = require('gulp'),
sass = require('gulp-sass'),
browsersync = require("browser-sync").create(),
function gulpSass() {
return gulp
.src('source/sass/**/*.sass')
.pipe(gulp.dest('source/css'))
.pipe(browsersync.stream())
}
function browserSync(done) {
browsersync.init({
injectChanges: true,
server: {
baseDir: "./"
},
port: 3000,
notify: false
});
done();
}
function watchFiles(done) {
gulp.watch('source/sass/**/*.sass', gulp.parallel(gulpSass));
gulp.watch('source/css/**/*.css', reload);
gulp.watch('source/js/**/*.js', reload);
gulp.watch('*.html', reload);
done();
}
const watch = gulp.parallel(watchFiles, browserSync);
exports.watch = watch;
function reload(done) {
browsersync.reload();
done();
}