Clarification On The Inability Of Javascript Deleting Inherited Properties.

guys. I'm studying up on properties for objects and one thing caught my eye on a source of info. There was this one part of the whole document that stated this about JS. Prototype

Solution 1:

delete removes a property from an object. If the object inherits the property rather than having its own property with that name, calling delete on the property doesn't do anything: You can't remove something that isn't there. :-) It's the object's prototype (or its prototype, or its prototype's prototype, etc.) that has the property, not the object inheriting it.

An example would probably help. Consider:

// An object to use as a prototype
var p = {answer: 42};
// An object using `p` as its prototype
var o = Object.create(p);

console.log(p.answer);                   // 42
console.log(p.hasOwnProperty("answer")); // true
console.log(o.answer);                   // 42
console.log(o.hasOwnProperty("answer")); // false

p has the property, not o; o just inherits it. Like this:

                          +−−−−−−−−−−−−−−−+
p−−−−−−−−−−−−−−−−−−−−−−+−>|   (object)    |
                       |  +−−−−−−−−−−−−−−−+
                       |  | [[prototype]] |−−−>(Object.prototype)
                       |  | answer: 42    | 
     +−−−−−−−−−−−−−−−+ |  +−−−−−−−−−−−−−−−+
o−−−>|    (object)   | |
     +−−−−−−−−−−−−−−−+ |
     | [[Prototype]] |−+
     +−−−−−−−−−−−−−−−+

So delete o.answer has no effect; o has no answer property for delete to remove. p is the object with answer.

If we remove the property from p (delete p.answer;), that will remove it — from p. And since prototypical inheritance is a live connection between an object and its prototype, asking o for answer after doing that will give us undefined, since o (effectively) asks p for it, and p doesn't have it anymore:

// An object to use as a prototype
var p = {answer: 42};
// An object using `p` as its prototype
var o = Object.create(p);

console.log(p.answer);                   // 42
console.log(p.hasOwnProperty("answer")); // true
console.log(o.answer);                   // 42
console.log(o.hasOwnProperty("answer")); // false

delete o.answer;                         // No effect
console.log(p.answer);                   // 42
console.log(o.answer);                   // 42

delete p.answer;                         // Removes it from p
console.log(p.answer);                   // undefined
console.log(o.answer);                   // undefined

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