JavaScript Object-Oriented programming: How to define property fields

We all know that the JS variable has a scope concept, so you can use this attribute to define the private field, and the initialization of the private field is mainly through the constructor.

For example, the following defines a read-only field first

function ListCommon2 (Afirst)  
 {  
   var first=afirst;  
   This. Getfirst=function () defines a privileged method to access the Read field {return a       
      ;}     
 Listcommon2.prototype.do2=function ()  
 {         
     var field= this. GetFirst ();//Read field alert in the instance method using the privileged method  
     ;  
 }    
             
     function test () {  
                //test code  
             var t2=new ListCommon2 ("Boiling water 2");            
             T2.do2 ();//                  
     }

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Of course, if you need a method to modify a field, you can also define a privileged method that is similar to reading a field.

As follows:

function ListCommon2 (Afirst)  
 {  
   var first=afirst;  
   This. Getfirst=function () defines a privileged method to access the Read field {return a.  
    }   
    This. Setfirst=function (NewValue)//defines a privileged method to set the field  
    {return       
      first=newvalue  
    }     
 } Listcommon2.prototype.do2=function ()  
 {         
     var field= this. GetFirst ();//Read field alert in the instance method using the privileged method  
     ;  
 }    
             
     function test () {  
                //test code  
             var t2=new ListCommon2 ("Boiling water 2");            
             T2. Setfirst ("test");//Reset field  
             t2.do2 ();//                  
     }

So the definition field can define local variables in the constructor, using the privileged method as a way to read and set fields, which can be accessed indirectly through privileged functions.