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Challenge: Solution Review

This lesson will explain the solution to the problem from the last coding challenge.

Node.js

function HomeLoan(amount,duration){
  this.amount = amount
  this.interest = 0.08
  this.duration = duration
  this.calculateInterest = function(){
    return this.amount*this.interest*this.duration
  }
}
function StudentLoan(amount,duration){
  this.amount = amount
  this.interest = 0.03
  this.duration = duration
  this.calculateInterest = function(){
    return this.amount*this.interest*this.duration
  }
}
function PersonalLoan(amount,duration){
  this.amount = amount
  this.interest = 0.05
  this.duration = duration
  this.calculateInterest = function(){
    return this.amount*this.interest*this.duration
  }
}
function Loans(){
  this.getloan = function(type,amount,duration){
    var loan;
    switch(type){
      case 'home':
        loan = new HomeLoan(amount,duration)
        break;
      case 'student':
        loan = new StudentLoan(amount,duration)
        break;
      case 'personal':
        loan = new PersonalLoan(amount,duration)
        break;
      default :
        loan = null
        break;
    }
    return loan
  }
}
var loan = new Loans()
 
var homeLoan = loan.getloan('home',3200,5)
console.log(homeLoan.calculateInterest())
 
var studentLoan = loan.getloan('student',1800,4)
console.log(studentLoan.calculateInterest())
 
var personalLoan = loan.getloan('personal',1200,2)
console.log(personalLoan.calculateInterest())

If you follow the diagram and the code, you’ll see that there is an abstract Loans constructor function. Its purpose is to instantiate an instance of a specific loan constructor depending on the parameters given.

From the diagram above, you can see that three types of loan objects can be instantiated:

PersonalLoan
StudentLoan
HomeLoan

These loans, in turn, have different types available. In our coding challenge, we do not go into these sub-categories; however, knowing this will help you in visualizing the overall picture.

Coming back to our code. Let’s start by understanding how Loans is following an abstract pattern.

Inside the Loan function, we first define the getloan method.
```
function Loans(){
 this.getloan = function(type,amount,duration){
     //code
 }
}
```
As you can see, it accepts the parameters type, amount, and duration.
Next, it defines the variable loan, which will store an instance of a specific loan at a given time.
```
var loan;
```
Depending on the type of loan required, the getloan function instantiates an instance of that loan. For example, if type equals home it instantiates HomeLoan instance.
```
loan = new HomeLoan(amount,duration)
```
The same goes for the student and personal type of loans.
In the end, the getloan function returns the specific loan instance.

Now let’s look at how the instance for a specific type of loan is created. As we discussed, we have three types, and the constructor for each is declared as follows:

function HomeLoan(amount,duration){
  //code..
}

function StudentLoan(amount,duration){
   //code..
}

function PersonalLoan(amount,duration){
   //code..
}

As mentioned in the question, all three contain the properties amount, interest, and duration. These properties are initialized in the body of the constructor.

function HomeLoan(amount,duration){
  this.amount = amount
  this.interest = 0.08
  this.duration = duration
}

function StudentLoan(amount,duration){
   this.amount = amount
   this.interest = 0.03
   this.duration = duration
}

function PersonalLoan(amount,duration){
   this.amount = amount
   this.interest = 0.05
   this.duration = duration
}

Since the interest parameter is fixed for each loan, we set its value to the specified number in the constructor.

Lastly, we define the calculateInterest method in the constructor of each loan.

this.calculateInterest = function(){
    return this.amount*this.interest*this.duration
}

Using the formula provided in the question, it multiplies the amount, the interest, and the duration of the current loan instance to calculate the final interest amount.

Now that the abstract pattern has been implemented, all you have to do to create an instance of a loan.

var loan = new Loans()
var homeLoan = loan.getloan('home',3200,5)

After creating an instance of Loans. Invoke the getloan method on it with the parameter that specifies the type of loan you want. This method will take care of the rest and create the required loan. You won’t need to use the new operator to create different types of loans yourself.

Challenge: Solution Review

Solution #

Explanation #