Why is gulp concat not working?

Question

JavaScript

there are two tasks:

gulp.task('concat', function() {
     return gulp.src(['application/assets/css/bootstrap.css',
                     'application/assets/css/bootstrap-material-design.min.css',
                     'application/assets/css/ripples.min.css',
                     'application/assets/js/lib/toastr/toastr.min.css',
                     'application/assets/fonts/ionicons/css/ionicons.min.css',
                     'application/assets/css/landing-page.css'])
         .pipe(concat('style.css'))
         .pipe(gulp.dest('application/assets/build/css/'));
});

gulp.task('js', function(){
    return gulp.src(['/application/assets/js/jquery-1.11.21.min.js',
                     '/application/assets/js/ripples.min.js',
                     '/application/assets/js/lib/toastr/toastr.min.js',
                     '/application/assets/js/bootstrap.min.js',
                     '/application/assets/js/textChange.js',
                     '/application/assets/js/material.js',
                     '/application/assets/js/lib/fancybox/jquery.fancybox.pack.js',
                     '/application/assets/js/lib/boxLoader/js/jquery.boxloader.min.js'])
        .pipe(concat('script.js'))
        .pipe(gulp.dest('application/assets/build/js/'));
});

The first one works, the second one doesn't.
the 'js' folder has been created, judging by the console everything works, but the script.js file does not appear.
Win 10.