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related: Confusion about protype chain , primitives and objects
in Firebug console :
a = 12
a.constructor.prototype.isPrototypeOf(a) // prints 'false'
I think this should print true
269
Every constructor has a prototype property, which will become the instance's [[Prototype]] when called via the new operator.
Each object has a private property which holds a link to another object called its prototype. That prototype object has a prototype of its own, and so on until an object is reached with null as its prototype. By definition, null has no prototype, and acts as the final link in this prototype chain.
So what's the difference between constructor and prototype? A short answer is that the constructor is a function that is used to create an object, while the prototype is an object that contains properties and methods that are inherited by objects created from a constructor.
All the objects have proto property. The prototype gives access to the prototype of function using function. proto gives access to the prototype of the function using the object.
a = 12 creates a primitive number, which is not quite the same as a Number object. Primitives are implicitly cast to objects for purposes of property access.
a = 12; //a is a primitive
b = new Number(12); //b is an object
a.constructor.prototype.isPrototypeOf(a); //false because a is primitive
b.constructor.prototype.isPrototypeOf(b); //true because b is an object
As per the ECMAScript spec:
When the
isPrototypeOfmethod is called with argument V, the following steps are taken:
- If V is not an object, return
false.
primitive numbers are not, strictly speaking, objects.
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