Javascript, code qui ne s'éxecute pas correctement.

function employee(nom, age) {

this.nom = nom;
this.age = age;

this.toText = function() {
        return this.nom + " (" + this.age + ")";
    }
}

var fred = new employee('Fred Flintstone', 32, 1970);
var john = new employee('Johnny Dep', 15, 1930); 

employee.prototype.salary=null;
fred.salary = 20000;
john.salary = 201893;

alert(fred.toText + '<br>' + fred.salary);
alert(john.toText + '<br>' + john.salary);