Of private method is defined in javascript

  • 2020-03-30 01:34:27
  • OfStack

I used to think that in the javascript world, all methods are public and you can't really technically define a private method.

var Person = function(name,sex){ 
    this.name = name; 
    this.sex = sex;      
    var _privateVariable = "";//Private variable & NBSP;      
    //Methods defined in the constructor are private methods
    function privateMethod(){    
        _privateVariable = "private value"; 
        alert(" Private method called! Private member value: " + _privateVariable);              
    privateMethod(); //A private method & NBSP can be called inside the constructor.                      

Person.prototype.sayHello = function(){ 
    alert(" Name: " + this.name + " Gender: " + this.sex); 

var p = new Person(" Yang guo under the bodhi tree "," male ");       

//p.privateMethod();// An error will be reported and private methods will not be invoked by the instance  
alert(p._privateVariable);//Display: undefined

Class constructor defined in the function, is a private method; Variables declared with var in constructors are also private variables. (however, there are differences between this and the notion of private members in strongly typed languages like c#, such as not being able to be called in methods other than constructors.)

Similarly, we can also implement the encapsulation of properties like set and get

var Person = function(){     
    var salary = 0.0; 

    this.setSalary = function(value){ 
        salary = value; 

    this.getSalary = function(){ 
        return salary; 

var p = new Person(); 

alert(p.getSalary());//Back to 1000
alert(p.salary);//Returns the undefined

Note: the concepts of "variable scope "," function call context (this)"," closure ", and" prototype chain "in js are all worth a bit of work.

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