JS Private Methods

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Private Methods

Why did that code work? An object's private variables can only be accessed by other methods that are part of that same object. So, we just used an object's public method to access a private variable!

Methods can also be private within a class and inaccessible outside of the class. Changing this.returnBalance from the last exercise to varreturnBalance makes this method private. If you run the program trying to access the method you get an undefinederror this time. 

The way to access a private method is similar to accessing a private variable. You must create a public method for the class that returns the private method.

Instructions

Create a method called askTeller within the Personclass that returns the returnBalance method. This means that it returns the method itself and NOT the result of calling that method. So you should NOT have parentheses after returnBalance. 

Because askTeller returns a method, we need to call it to make it any use. This is what var myBalance = myBalanceMethod(); does. 

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Hint

Your method should resemble how we defined getBalance last time—you should use this.askTeller = function() { }. Don't declare askTeller with var.


You return method the same way that you would return simple variables. Be careful not to call the method though and leave out parentheses in your return statement!


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wilber.shinobi的个人空间 引用 删除 wilber.shinobi   /   2015-08-15 14:21:14
function Person(first,last,age) {
   this.firstname = first;
   this.lastname = last;
   this.age = age;
   var bankBalance = 7500;
  
   var returnBalance = function() {
      return bankBalance;
   };
      
   // create the new function here
   //var askTeller = function() { // incorrect
   this.askTeller = function() {
       return returnBalance; // askTeller returns a method, we need to call it to make it any use.
   };
}

var john = new Person('John','Smith',30);
console.log(john.returnBalance);
var myBalanceMethod = john.askTeller();
var myBalance = myBalanceMethod();
console.log(myBalance);
 

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