var idCounter = 1;

function Employee(name, dept) {
   this.name = name || '';
   this.dept = dept || 'general';
   this.id = idCounter++;
}

function Manager(name, dept, reports) {...}
Manager.prototype = new Employee;

function WorkerBee(name, dept, projs) {...}
WorkerBee.prototype = new Employee;

function Engineer(name, projs, mach) {...}
Engineer.prototype = new WorkerBee;

function SalesPerson(name, projs, quota) {...}
SalesPerson.prototype = new WorkerBee;

var mac = new Engineer('Wood, Mac');