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.sayHello();

//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();

p.setSalary(1000);
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.