JavaScript prototype prototype understanding

First we must understand JS has several data types?

String number Boolean Object Null Undefined

Many other objects can be derived under Object objects

such as function Date Math array, etc.

I drew a picture of myself in a simple and rough way:

Red represents the object black represents the prototype object

Here are just a few points to keep in mind:

1, what are the objects that have prototype? function Array String Math object function etc some built-in objects

var student={
Name: ' Student ',
Grade: ' Class three ',

}
var b=new Object ();
Console.log (b.prototype);//undefined
var c= ' AAA ';
Console.log (c.prototype);//undefined
Console.log (String.prototype);//String common methods such as IndexOf

Why is it undefined because they're the objects that instantiate an object that is instantiated from an object is not a prototype object.

Therefore, you cannot use an instantiated object to. prototype

2,__proto__ is a property owned by each object, including an instantiated object, and the function is to find out which object the object derives from.

Console.log (c.prototype);//undefined
Console.log (c.__proto__);//string

Practice

Function Show () {
Alert (' Hello ');
}
Console.log (show.prototype);//object
Console.log (show.prototype.constructor);//function Show () {alert (' Hello ');}
Console.log (show.__proto__);//function () {}
Console.log (show.__proto__.__proto__);//object{}
Console.log (show.__proto__.__proto__.__proto__);//null
Array.prototype.show=function () {
Alert (' Hello ');
}
var arr=[1,2,3];
Arr.show ();//Instantiate an array also has a show method

JavaScript prototype prototype understanding