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JavaScript Practice Object Interaction Checking Out and Returning a Book Solution: Charging Fines to Patrons

Posted by Xun Huang
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Xun Huang
Web Development Techdegree Graduate 18,515 Points

WHY 'patron.balance += this.dailyFine * daysLate' ???

I don't understand , because getDate() means get the day of the month, it not a difference between now and the dueDate, it always returns a number between 1 and 31, and what if a patron overdue for 100 days? And why use '+=' instead of '=' , shouldn't we calculate an integer first then times the overdue day?

Caleb Kemp
Caleb Kemp
12,754 Points
Caleb Kemp
Caleb Kemp
12,754 Points

After checking out the code myself, it would seem that you are correct. You could tag the instructor and see if they have an explanation, but I'm of the opinion that it was probably just an oversight. Great job noticing that though.

1 Answer

Steven Parker
Steven Parker
231,007 Points
Steven Parker
Steven Parker
231,007 Points

The use of "+=" would add the fine to any current balance in the account, so that's probably intended.

But converting the difference between two dates into a date itself isn't really valid as a concept, though it might seem to work as long as the difference was less than a month. A more appropriate way to calculate a difference would be:

        // difference in ms / ms per day
        const daysLate = Math.floor((now.getTime() - patron.currentBook.dueDate.getTime())
                                    / (1000*60*60*24));

You might want to make a bug report directly to the staff as described on the Support page. If you're the first to report it, it should get you the special Exterminator badge. :beetle:

Xun Huang
.a{fill-rule:evenodd;}techdegree seal-36
Xun Huang
Web Development Techdegree Graduate 18,515 Points

Thank you! That makes much more sense!