How to use JavaScript to implement Class Functions

Some time ago, after learning "ajax self-taught manual", I realized that javascript can still be written like this.

 I have learned the concepts of classes in Java, C #, and VB, and classes have functions such as inheritance, encapsulation, and polymorphism. Javascript is not an object-oriented language, but an explanatory language.

But we can also use JavaScript to implement inheritance and polymorphism.

 Javascript implementation class, there are multiple methods.

Method 1: constructor.

Code

  Function  Coder (){
 This  . Name  =     '  John  '  ;
  This  . Job  =     '  ProgramEmployee  '  ;
  This . Coding  =     Function  ()
{
Alert (  '  I'm writingCode  '  );
}
}

  VaR  Coder  =  New  Coder ();
Alert (CODER. Name );
Coder. coding (); 

 

 Method 2: Factory method.

Code

 Function  Createcoderfactory (){
  VaR  OBJ  =  New  Object ();
OBJ. Name  =     '  John  '  ;
OBJ. Job =     '  Programmer  '  ;
OBJ. Coding  =     Function  (){
Alert (  '  I am writing code  '  );
};
  Return  OBJ;
}
  VaR Coder  =  Createcoderfactory ();
Alert (CODER. Name );
Coder. coding ();
 

However, both the factory method and constructor method share the same disadvantage, that is, every function of this class is instantiated every time an instance is created. 

 Method 3: prototype chain.

Code

  Function  Coder (){}
Coder. Prototype. Name  =    '  John  '  ;
Coder. Prototype. Job  =     '  Programmer  '  ;
Coder. Prototype. Coding  =     Function  (){
Alert (  '  I am writing code  ' );
};
  VaR  Coder  =     New  Coder ();
Alert (CODER. Name );
Coder. coding (); 

Note: The book says: the disadvantage of prototype chain is that all its attributes are shared, and all other attributes of a prototype chain will change as long as one instance changes.The test is as follows:

  VaR  Coder1  =    New  Coder ();
  VaR  Coder2  =     New  Coder ();
Alert (coder1.name );  /*  Show "Wang"  */  
Coder2.name  =     '  Old Wang  ' ;
Alert (coder1.name );  /* This shows "Xiao Wang". If it says in the book, it should show "Lao Wang "*/  
Alert (coder2.name );  /*  This shows "Old Wang"  */  
 

Alert (coder1.name); if "Old Wang" is displayed in the book, but "Little Wang" is displayed here, an error occurs in the book.

  

Method 4: hybrid mode.

The above three methods all have their own shortcomings, so we need to improve them.

  Function  Coder (){
  This  . Name  =     '  John  '  ;
  This  . Job  =     ' Programmer  '  ;
}
Coder. Prototype. Coding  =     Function  (){
Alert (  '  I am writing code  '  );
}; 

 

Method 5: Dynamic Source chain.

There is another way to solve the first three shortcomings.

Code

  Function  Coder (){
  This  . Name  =     '  John  '  ;
  This  . Job  =    '  Programmer  '  ;
  If  (  Typeof  (CODER. _ init)  =     '  Undefined  '  ){
  This  . Coding  =    Function  ()
{
Alert (  '  I am writing code  '  );
};
  This  . _ Init  =     True  ;
}
} 

what about this method, when used for the first time, because _ init is not initialized, the following code is executed to instantiate the coding function. It will not be executed in the future, so that the function will be instantiated only once.