Browsersync won't start

When I write in terminal "gulp browsersync" I see how it "starting 'browsersync'..." but nothing happens. My code looks like :

//On BrowserSync 
const browserSync = require('browser-sync').create();
function browsersync() {
    browserSync.init({
        server: {baseDir: 'app/'},
        notify: false,
        online: true
    })
}
    
exports.browsersync = browsersync;