如何将原型属性从javascript中的超类委托给子类

Question

Please help me to understand following code snippet.

var ob = {a:20,b:30};
Object.prototype.c = '40';
for (var x in ob){
    console.log(x); // will log a,b,c in console
}
var keys = Object.keys(ob) ;
console.log(keys); // will log a,b in console

My question is that , How putting property 'c' on the prototype of 'Object' will make it available to 'ob' ?

Edit: Basically I want to know which default constructor function is called when we try to create an object and what are the basic responsibilities performed by the constructor ?

Answer 1

The Object.keys() method returns an array of a given object's own enumerable properties, the difference being that a for-in loop enumerates properties in the prototype chain as well, so Object.keys(ob) will enumerate only ob own property not the property of ob prototype

Object Properties

Object.prototype.constructor --> Specifies the function that creates an object's prototype.

Object.prototype.__proto__ --> Points to the object which was used as prototype when the object was instantiated.

Object.prototype.__noSuchMethod__ --> Allows a function to be defined that will be executed when an undefined object member is called as a method.

Answer 2

An object literal ( {} ) will inherit from Object.prototype . Object.prototype.c = '40'; sets the c property on Object 's prototype, so all objects inheriting from Object will be able to access this property. Any properties defined on Object 's prototype will be accessible on objects inheriting from it.

The difference between for (var x in ob) and Object.keys(ob) is that Object.keys(ob) will return only the properties of the ob object, whereas for (var x in ob) will traverse the prototype chain and find the c property on Object 's prototype.

By default, no properties defined on Object 's prototype will be included in a for-in loop as they are not enumerable. An added property is enumerable by default.