Demo of JavaScript constructor property. Illustrates that the constructor property is set automatically by JavaScript, but is overwritten when a custom prototype is assigned, necessitating the constructor to be explicitly set in the prototype. For more info, refer to http://nerdstuckathome.wordpress.com/2012/11/06/a-quick-digression-about-the-co…

constructorDemo.js

function Nuttin() {};

function Sumtin() {};
Sumtin.prototype = { foo: function(){} };

function SumtinElse() {};
SumtinElse.prototype = { bar: function(){}, constructor: SumtinElse };

function AnotherSumtinElse() {};
Object.defineProperty(AnotherSumtinElse, "prototype", { value: {bar: function(){}, constructor: AnotherSumtinElse }});

Nuttin.constructor;
// function Function() { [native code] }

Sumtin.constructor;
// function Function() { [native code] }

SumtinElse.constructor;
// function Function() { [native code] }

AnotherSumtinElse.constructor
// function Function() { [native code] }

Nuttin.prototype.constructor;
// function Nuttin() {}

Sumtin.prototype.constructor;
// function Object() { [native code] }

SumtinElse.prototype.constructor;
// function SumtinElse() {}

AnotherSumtinElse.prototype.constructor
// function AnotherSumtinElse() {}

var n = new Nuttin();
n.constructor;
// function Nuttin() {}

var s = new Sumtin();
s.constructor;
// function Object() { [native code] }

var se = new SumtinElse();
se.constructor;
// function SumtinElse() {}

var ase = new AnotherSumtinElse();
ase.constructor;
// function AnotherSumtinElse() {}


// fascinating detail
// explicit setting of constructor makes the property enumerable
// from: http://nerdstuckathome.wordpress.com/2012/11/06/a-quick-digression-about-the-constructor-in-javascript/
for (key in Nuttin.prototype) { console.log(key) };
// undefined

for (key in Sumtin.prototype) { console.log(key) };
// foo

for (key in SumtinElse.prototype) { console.log(key) };
// bar
// constructor

for (key in AnotherSumtinElse.prototype) { console.log(key) };
// undefined