SOURCE

function Employee (name,dept) {
  this.name = name || "";
  this.dept = dept || "general";
}

function WorkerBee(name,dept,projs) {
  Employee.call(this, name, dept)
  this.projects = projs || [];
}


WorkerBee.prototype = new Employee;

function Engineer (name, projs, mach) {
  WorkerBee.call(this, name, "engineering",projs)
  this.machine = mach || "";
}

Engineer.prototype = new WorkerBee;
var jane = new Engineer("Doe, Jane", ["navigator", "javascript"], "belau");

Employee.prototype.specialty = "none";

function instanceOf(object, constructor) {
   while (object != null) {
      if (object == constructor.prototype)
         return true;
      object = object.__proto__;
   }
   return false;
}
// console.log(jane instanceof Engineer)
console.log(instanceOf(jane, Engineer))
// console.log(jane.__proto__)
console.log(jane)