const a = ['Pro', 'To', 'Turk'];

console.log(a.join());      // "Pro,To,Turk"
console.log(a.join(', '));  // "Pro, To, Turk"
console.log(a.join(' + ')); // "Pro + To + Turk"
console.log(a.join(''));    // "ProToTurk"