A good article about javascript-prototype inheritance _ prototype

A good article about javascript-prototype inheritance 1. The most basic usage is to assign an instance of ClassA to ClassB,
ClassB inherits all the attributes of ClassA.
Code entry:

Script function ClassA () {this. a = 'a';} function ClassB () {this. B = 'B';} ClassB. prototype = new ClassA (); var objB = new ClassB (); for (var p in objB) document. write (p + ""); script
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2. From the perspective of prototype Inheritance theory,
The prototype inheritance of js is a reference prototype, not a copy prototype,
Therefore, modifying the prototype will cause changes to all B instances.
The Code is as follows:

Script function ClassA () {this. a = 'a';} function ClassB () {this. B = 'B';} ClassB. prototype = new ClassA (); var objB = new ClassB (); alert (objB. a); ClassB. prototype. a = 'changed !! '; Alert (objB. a); script
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3. However, write operations on subclass objects only access members of subclass objects,
They do not affect each other. Therefore,
Write is the write subclass. Read is the read prototype (if not in the subclass ).

Script function ClassA () {this. a = 'a';} function ClassB () {this. B = 'B';} ClassB. prototype = new ClassA (); var objB1 = new ClassB (); var objB2 = new ClassB (); objB1.a = '!!! '; Alert (objB1.a); alert (objB2.a); script
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4. Each subclass object is referenced by the same prototype,
Therefore, the prototype members in the subclass object are actually the same.

Script function ClassA () {this. a = function () {alert () ;};} function ClassB () {this. B = function () {alert () ;};} ClassB. prototype = new ClassA (); var objB1 = new ClassB (); var objB2 = new ClassB (); alert (objB1.a = objB2.a); alert (objB1. B = objB2. B ); script
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5. When a subclass is constructed, the prototype constructor will not be executed.

Script function ClassA () {alert ("a"); this. a = function () {alert () ;};} function ClassB () {alert ("B"); this. B = function () {alert () ;};} ClassB. prototype = new ClassA (); var objB1 = new ClassB (); var objB2 = new ClassB (); script
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6. The next step is fatal. Access the prototype member object in the subclass object:

Script function ClassA () {this. a = [];} function ClassB () {this. B = function () {alert () ;};} ClassB. prototype = new ClassA (); var objB1 = new ClassB (); var objB2 = new ClassB (); objB1.a. push (, 3); alert (objB2.a); // All a members in all B instances have changed !! Script
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7. Therefore, no member object exists in the prototype inheritance prototype class! All members must be value-type data (string can also be)
Using prototype inheritance has the advantages of high execution efficiency, no waste of memory, dynamic addition of methods for the parent class, and so on in the subclass.

8. prototype inheritance is inherited by setting prototype of the subclass to an instance of the parent class.

9. prototype inheritance also has four obvious disadvantages:
Disadvantage 1: The constructor of the parent class is not executed when the subclass is instantiated as in JAVA, but executed only once when the inheritance is set. This is often not what we want, especially when the constructor of the parent class has some special operations.
Disadvantage 2: The constructor of the parent class is not executed when the child class is instantiated, the member variables set in the constructor of the parent class become the public variables of all instance objects when they are in the subclass. Because the inheritance in JavaScript only occurs when the value of the "get" attribute is "String", the data of the attribute value "String", "Number", and "Boolean" cannot be modified. However, the Array and Object types are problematic.
Disadvantage 3: If the constructor of the parent class requires a parameter, there is no way.
Disadvantage 4: The original prototype object of the subclass is replaced, and the constructor attribute of the subclass is no longer available. When an instance of the class obtains its constructor attribute, it obtains the constructor attribute inherited from the parent class, so that the constructor value is the parent class rather than the Child class.

10. prototype defects can be modified.
For example, it is convenient to write it as a Function object.

Function. prototype. Extends = function (parentClass)
{
Var Bs = new Function ();
Bs. prototype = parentClass. prototype;
This. prototype = new Bs ();
This. prototype. Super = parentClass;
This. prototype. constructor = this;
}

I hope you will be able to introduce your js experts in a better way.
For the 3,6

Script function ClassA () {this. a = [] this. aa = 100;} function ClassB () {this. B = function () {return "classbb"};} ClassB. prototype = new ClassA (); var objB1 = new ClassB (); var objB2 = new ClassB (); objB1.a. push (10100, 3); objB1.aa = alert (objB2.a); alert (objB2.aa); script
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For inheritance,
Array. prototype cannot inherit ClassA, ClassB

Script function ClassA () {this. a = [] this. aa = 100;} function ClassB () {this. B = function () {return "classbb"};} ClassB. prototype = new ClassA (); Array. prototype = new ClassB (); var _ array = new Array () alert (_ array. B () script
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Inheritance with Parameters

<P id = "a"> aaa </p> script function ClassB () {this. B = function () {return "classbb" };} function ClassC (R) {el = document. getElementById (R) return el} ClassB. prototype = new ClassC () var st = new ClassB () alert (st (""). innerHTML) script
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