Débutant javascript

var maVoyelle= function(lettre) {

var voyelle = ["a", "e", "i", "o", "u"];

for(var i in voyelle){

    if(lettre === i){
        return true;
    } else {
        return false;
    }
}

};

maVoyelle("a");

var book = ["bill Gates","The Road Ahead","21/07/2021","true"];

book.unshift("1");

console.log("id :"+ book[0]);
console.log("auteur :" + book[1]);
console.log("titre :" + book[2]);
console.log("date d'achat :" + book[3]);
console.log("Etat de lecture :" + book[4]);