Gulp watch - not working - gulp

Question

I have gulpfile.js from https://github.com/gulpjs/gulp.
I just change folders name for mine.
Task 'gulp' work normally, first 'gulp watch' too. But any another save any less file don't do anything. Just "Finished 'styles' after 1.34 s"
(JS works good)
Any advice?
main.less have less imports with all filles
Folders looks like:
/www
/js
/css
main.less
file.less
file2.less
/lib
file3.less
var gulp = require('gulp');
var less = require('gulp-less');
var babel = require('gulp-babel');
var concat = require('gulp-concat');
var uglify = require('gulp-uglify');
var rename = require('gulp-rename');
var cleanCSS = require('gulp-clean-css');
var del = require('del');
var paths = {
styles: {
src: 'www/css/main.less',
dest: 'www/css/'
},
scripts: {
src: 'www/js/js/**/*.js',
dest: 'www/js/'
}
};
function clean() {
return del([ 'assets' ]);
}
function styles() {
return gulp.src(paths.styles.src)
.pipe(less())
.pipe(cleanCSS())
// pass in options to the stream
.pipe(rename({
basename: 'main',
suffix: '.min'
}))
.pipe(gulp.dest(paths.styles.dest));
}
function scripts() {
return gulp.src(paths.scripts.src, { sourcemaps: true})
.pipe(babel())
.pipe(uglify())
.pipe(concat('all.min.js'))
.pipe(gulp.dest(paths.scripts.dest));
}
function watch() {
gulp.watch("www/js/js**/*.js", scripts);
gulp.watch("www/css/**/*.less", styles);
}
exports.clean = clean;
exports.styles = styles;
exports.scripts = scripts;
exports.watch = watch;
var build = gulp.series(clean, gulp.parallel(styles, scripts));
gulp.task('build', build);
gulp.task('default', build);

Answer 1

As #Jakub thought, you never actually call your watch task in the code you presented! You probably want something like this:
var build = gulp.series(clean, gulp.parallel(styles, scripts), watch);