Problems with constructors in JS

gistfile1.txt

// 1) it is dangerous to have a `constructor` property, but not forbidden

function Car(model){ 
   this.model = model; 
   this.speed = 0; 
} 

function Car2(model, constructor){ 
   this.model = model; 
   this.constructor = constructor; 
   this.speed = 0; 
} 

var golf = new Car("Golf"); 
golf.constructor === Car; // true 
 
var golf2 = new Car2("Golf", "Volkswagen"); 
golf2.constructor === Car2; // false !

// 2) forgetting the new operator does not throw error, but can cause huge collateral damage

var toyota = Car("Toyota","Yaris"); // oops, forgetted new
console.log(window.model); // Yaris ; now we have a global leak
console.log(window.constructor); // Toyota ; oh shit, we also overridden Window. Greeeat

// 3) instanceof can be fooled in multi DOM environments: http://perfectionkills.com/instanceof-considered-harmful-or-how-to-write-a-robust-isarray/

// 4) instance can be fooled by reference to another prototype

function foo() {}
var bar = { a: ‘a’};
foo.prototype = bar; // Object {a: “a”}
baz = Object.create(bar); // Object {a: “a”}
baz instanceof foo // true. oops.