... en action

Voici un élégant moyen de remplacer concat.

const T1 = ["Dupont", "Whells", "toto"];

const T2 = ["Dupond", "Whells", "titi"];

console.log(T1);
console.log(...T1);
console.log( [...T1 , ...T2] );



const promos = [
  { promo: "L3miage", etudiants: ["Dupont", "Whells", "Toto"]},
  { promo: "L2miage", etudiants: ["Dupond", "Pathé"]},
  { promo: "M1miage", etudiants: ["Audu", "Baby"]},
]

const tousEtudiants = promos.reduce(function(prev, curr) {
  return [...prev, ...curr.etudiants];
},[]);

console.log(tousEtudiants.sort());