JavaScript Object-oriented Inheritance, javascript object-oriented

JavaScript Object-oriented Inheritance, javascript object-oriented

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Javascript is object-oriented and can reflect its inheritance.
...... JS is only based on object-oriented, rather than the real object-oriented, because the three main features of object-oriented: encapsulation. Inheritance and polymorphism!

Javascript inheritance gets dizzy.
This is a typical JavaScript prototype chain Inheritance Problem.

I. JavaScript object-oriented World View
In JavaScript, all except the five original data types are objects, including function objects;
JavaScript does not have the concept of classes, but only functions and prototypes. Some JavaScript articles will mention classes. This is just a metaphor. Compared with the class-based language (Java, C #), it can be understood as a class, but it is definitely not a class;
JavaScript is not a class-based Object-oriented Inheritance, but a prototype-Based Object-Oriented inheritance. The implementation principle mainly depends on the prototype chain mechanism of JavaScript;

The above are the basic principles of JavaScript. If you understand it, you can continue.

Ii. Differences between functions and objects
// This is a function declaration. According to the above principle, Person is a function object, function Person () {}// this is a direct volume object creation, use {} to directly create an object and assign a value to obj to reference var obj = {};

Iii. Differences between constructors and functions

In JavaScript, apart from functions, there is also a concept called constructor. Do not be fooled by this name. constructor is a function. There is no difference in nature, but it is just an ideological thing. A constructor can distinguish functions from each other directly by name, as shown below:
Function fn1 () {} fn1 (); // The fn1 function is just a call, so it is just a common function Klass () {} new Klass (); // Klass is instantiated using the new operator, so we call it a constructor. // Similarly, if we want fn1 to be instantiated, it can also be called fn1 as the constructor new fn1 ();
However, JavaScript is still used to class-based naming. constructors start with uppercase letters and treat them as a class.

Iv. Differences between function objects and objects

For example, the question of the subject:
// This is a Function object, which is an instance object of the constructor (Function) // Note: The Constructor (function) and the above Function object are written here, function Person () {}// this is an Object. It is an instance Object var obj ={} of the constructor (Object). // At the same time, the constructor (Function) object is a function Object.
Only function objects can be instantiated using the new operator:
New Person (); // This is The new obj () that works; // the JavaScript engine throws an exception "TypeError: object is not a function"

V. Differences between prototype and _ proto _

Prototype: prototype is a prototype object. Only function objects have this property. prototype is also an object.

_ Proto _ is a private attribute of all JavaScript objects. __proto _ is read-only. Both common objects and function objects have the _ proto _ attribute.

_ Proto _ points to the prototype object of its constructor:
// Obj is the Instance Object of the constructor (Object), so console. log (obj. _ proto _ = Object. prototype); // true // Person is the Function of the constructor ...... remaining full text>