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In-Depth Information

Table 10-16 Mortgage Loan Test Data Set

Data Set

Sales Price

Down Payment

Interest Rate %

Years

Comment

1

23000

4.75

20

The sales price is not

a valid number!

2

123900

24800

A

15

The interest rate is not

a valid number!

3

190000

19000

3.75

30

No error messages

4

231000

45000

5.375

Please select a valid

number from the list

(10, 15, 20, or 30)!

Refresh button

no value selected

from number of years

drop-down list causes

alert box to display

error message

validation logic does not place

result in monthly payment text

field if there is an error; an

error keeps user on the text

field or drop-down menu

user clicks OK

button to re-enter

data as indicated

Figure 10-23

Plan

Ahead

Calculating the monthly payment.

The monthlyPmt() function requires three parameters: the loan amount (loanAmt), the interest

rate (loanRate), and the number of years that the payments will be made (loanYears). These

values are passed from the CalcLoanAmt() user-defined function to the monthlyPmt() function.

The steps to calculate the monthly payment are as follows:

1. Pass the three variables — loanAmt, loanRate, and loanYears — to the monthlyPmt()

function.

2. Convert the annual interest rate to a monthly interest rate (interestRate) by dividing

loanRate by 1200

3. Convert the number of years to the number of months of payments (Pmts) by

multiplying loanYears by 12

4. Calculate the monthly payment with the following formula:

loanAmt * (interestRate / (1 - (1 / Math.pow(1+interestRate,Pmts))))

5. Return the monthly payment as a fixed decimal value to two decimal places using the

toFixed(2) method.