What is the target of the `__proto__` attribute in a constructor function?

I'm taking the time to dive deeper into prototypal inheritance. I know that an instance's __proto__ property points to the constructor function's prototype object, but where does the constructor function's __proto__ property point to?

I initially thought that since the constructor function is also an instance of Function, it would point to the Function constructor's prototype object. However, it turns out to be an empty function.

var Example = function(){
   this.attribute = 'example';
}

var exampleInstance = new Example();

exampleInstance.__proto__ === Example.prototype // true
Example.__proto__ // function() {}

[Edit] Ovidiu Dolha has now validated my understanding, so perhaps this will be beneficial for someone else.

https://i.sstatic.net/Lr44S.jpg

Answer №1

Instance.exampleProto will be identical to Prototype.function, just as sample.__proto__ is equivalent to Instance.prototype

This occurs because Instance is a type of Function.

Eventually, everything will trace back to Object.prototype, which serves as the core in terms of prototypal inheritance.

It's worth noting that it's recommended to avoid using __proto__ whenever possible, as it is now considered deprecated. Instead, opt for Object.getPrototypeOf()

Answer №2

There is a prototype chain that extends all the way to the "Object" as the ultimate root.

According to the ECMAScript 5.1 specification, it is defined as follows:

Section 15.3.4 Properties of the Function Prototype Object:

The [[Prototype]] internal property value of the Function prototype object is the default built-in Object prototype object.

Additionally, in Section 15.2.4 Properties of the Object Prototype Object:

The [[Prototype]] internal property value of the Object prototype object is set to null.

You can test this in your console.

console.log(exampleInstance);

Example
attribute: "example"
__proto__: Object
constructor: ()
__proto__: Object
__defineGetter__: __defineGetter__()
__defineSetter__: __defineSetter__()
__lookupGetter__: __lookupGetter__()
__lookupSetter__: __lookupSetter__()
constructor: Object()
hasOwnProperty: hasOwnProperty()
isPrototypeOf: isPrototypeOf()
propertyIsEnumerable: propertyIsEnumerable()
toLocaleString: toLocaleString()
toString: toString()
valueOf: valueOf()
get __proto__: __proto__()
set __proto__: __proto__()

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