How can I see the prototype chain of a Javascript object?

Question

Given the following code:

function a() {} function b() {} b.prototype = new a(); var b1 = new b(); 

We can stay that a was added to the b prototype chain. Fine. And that's right:

 b1 instanceof b b1 instanceof a b1 instanceof Object 

My question is: what if we do not know the origin of b1 in advance? How can we find members of our prototype chain? Ideally, I need an array like [b, a, Object] or ["b", "a", "Object"] .

Is it possible? In my opinion, I saw an answer somewhere on SO that described how to find out, but I can't let life find me again.

Answer 1

Well, the prototype of the communication between objects ( [[Prototype]] ) is internal, some implementations, such as Mozilla, display it as obj.__proto__ .

Object.getPrototypeOf method of ECMAScript 5th Edition is what you need, but it is not implemented right now on most JavaScript engines.

Look at this John Resig implementation , it has a trap, it relies on the constructor property for engines, t __proto__ :

 if ( typeof Object.getPrototypeOf !== "function" ) { if ( typeof "test".__proto__ === "object" ) { Object.getPrototypeOf = function(object){ return object.__proto__; }; } else { Object.getPrototypeOf = function(object){ // May break if the constructor has been tampered with return object.constructor.prototype; }; } } 

Remember that this is not 100% more reliable, as the constructor property is changed on any object.

Answer 2

You can use the constructor property of an object to find the prototype there, and then scroll through it until you reach the end of the rainbow.

 function getPrototypes(o) { return (function gp(o, protos) { var c = o.constructor; if (c.prototype) { protos.push(c.prototype); return gp(c.prototype, protos); } return protos; })(o, []); } 

(maybe) (or maybe not :-) give me a second) (well shit, I think it's possible, but ignore this code)

[edit] wow, this blows my head completely - this function closes, but not quite right; prototyping is weird, and I feel scared and lonely. I suggest paying attention only to the amazing @CMS above.

Answer 3

Here is the starting point:

 Object.prototype.getConstructorNames=function(){ return Object.keys(window).filter(function(e){ return typeof window[e]==="function" && this instanceof window[e]},this) } 

Of course, this is really incomplete, but I think that it will work in most cases, and if someone wants to add to it, he can.