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playing around with an `Object.make()` helper
// `Object.make(..)` is a helper/wrapper for `Object.create(..)`. Both create a new
// object, and optionally link that new object's `[[Prototype]]` chain to another object.
// But `Object.make(..)` makes sure the new object always has a `__proto__` property
// (even a null one) and delegation to a `isPrototypeOf(..)` method, both of which are
// missing from the bare object (aka "Dictionary") created by `Object.create(null)`.
// `isPrototypeOf()` is put on a extra object that your created object can delegate to,
// if any only if you create an empty object (by not passing a `linkTo`) that otherwise
// wouldn't have access to `isPrototypeOf()`.
// `__proto__` is only imparted if you're in a non-`__proto__` engine (IE<=10, etc), OR
// if the object in question doesn't eventually delegate to the `Object.prototype` (and
// thus doesn't have access to the special `Object.prototype.__proto__`), like for instance
// a "Dictionary" created by `Object.create(null)` (whose `[[Prototype]]` is null).
// The particular reason for making sure at least a read-only (not settable) `__proto__`
// is always present (or delegatable to) is so that an effective/simple non-ES5 polyfill
// for `Object.getProtoypeOf()` can be made and used.
if (!Object.make) {
Object.make = function(linkTo) {
// if no `linkTo` provided, make a substitute delegate ancestor
// that only has `isPrototypeOf()` in it.
if (!linkTo) {
linkTo = Object.create(null);
linkTo.isPrototypeOf = Object.isPrototypeOf;
var obj = Object.create(linkTo);
// impart a `__proto__` property, if one doesn't exist (or can't be
// delegated to) already on the new object
if (!("__proto__" in obj) || Object.make.__proto_needed__) {
// can we ES5'ify a non-enumerable property for `__proto__`?
if (Object.defineProperty) {
enumerable: false,
writable: false,
value: linkTo
// oh well, just add it directly
else {
obj.__proto__ = linkTo;
return obj;
// FT for non __proto__ engines
Object.make.__proto_needed__ = !("__proto__" in {});
// non-ES5 polyfill for `Object.getPrototypeOf(..)`
// NOTE: relies on `__proto__` being present, which `Object.make(..)` above ensures
if (!Object.getPrototypeOf) {
Object.getPrototypeOf = function(obj) {
return obj.__proto__ || null;
// examples:
var Foo = Object.make(); = "Foo";
Foo.identify = function() {
console.log("Me: " +;
var Bar = Object.make(Foo); = "Bar";
var bar1 = Object.make(Bar); = "bar1";
var bar2 = Object.make(Bar); = "bar2";
Foo.identify(); // "Me: Foo"
Bar.identify(); // "Me: Bar"
bar1.identify(); // "Me: bar1"
bar2.identify(); // "Me: bar2"
Foo.isPrototypeOf(Bar); // true
Bar.isPrototypeOf(bar1); // true
Bar.isPrototypeOf(bar2); // true
Foo.isPrototypeOf(bar1); // true
Foo.isPrototypeOf(bar2); // true
Object.getPrototypeOf(Bar) === Foo; // true
Object.getPrototypeOf(bar1) === Bar; // true
Object.getPrototypeOf(bar2) === Bar; // true

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getify commented Mar 26, 2013

A good question was asked: why is __proto__ being added here if not being used in this code example. I don't show it here, but I also prefer to have a non-ES5 polyfill for Object.getPrototypeOf(..).

if (!Object.getPrototypeOf) {
   Object.getPrototypeOf = function(obj) {
      return obj.__proto__ || null;

edit: I've now added examples of __proto__ being useful for polyfill'ing Object.getPrototypeOf(..) and how that is useful in inspecting the [[Prototype]] link chain.


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lsmith commented Apr 2, 2013

Shouldn't __proto__ be defined with Object.defineProperty? You don't want it enumerable, do you? And setting it should have side effects, no?


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getify commented May 1, 2013

@lsmith I have updated the snippet to use a different technique for both __proto__ and isPrototypeOf(), after playing with it more.

However, I have not opted to try and actually polyfill the magical behavior (the set'ability) of __proto__ in this case. Others have created a set setter for it, I believe, but I think there are many caveats to it, not the least of which is you can't actually mimic that in browsers that don't already have __proto__, so making it seem like you support that when you can't is _worse_, IMHO, than just not supporting it outright.

Basically, I'm making sure __proto__ is added only so that there's an easy polyfill for Object.getPrototypeOf().


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wilmoore commented May 7, 2013

...making sure proto is added only so that there's an easy polyfill for Object.getPrototypeOf().

For those that may happen across this and wonder what the __proto__ part of the conversation is about, see my original question, which asks:

Unless I am missing something simple, don’t we have a minor x-browser issue? The Foo object has no .constructor property and __proto__ is not available everywhere. This makes it difficult to properly polyfill Object.getPrototypeOf.

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