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

Samuel Kleos
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Samuel Kleos
Front End Web Development Techdegree Student 13,483 Points
Posted by Samuel Kleos
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Samuel Kleos
Front End Web Development Techdegree Student 13,483 Points

Confusion. . . 😵‍💫 Why is my daysOverDue property negative?

In my Library class I used filter and reduce to generate a .daysOverDue value from a book using a getter method in the book class. Also, a setter method out() is used to set .dueDate to -14 days (in the past): 

chargeFines() {
    const now = new Date();

    const latePatrons = this.patrons.filter(patron => 
        (patron.currentBook !== null && patron.currentBook.dueDate < now)
    );

    for (let patron of latePatrons) {
        const daysLate = Math.floor( (now.getTime() - patron.currentBook.dueDate.getTime()) / (1000 * 60 * 60 * 24));
        patron.balance += this.dailyFine * daysLate;
    }
}

My solution:

collectFines() {
        let today = new Date();
        console.log(today.getDate())
        return this.patrons
            .filter(patron => (patron.currentBook.daysOverDue > 0))
            .reduce((collector, patron) => { 
                console.log(patron.currentBook.dueDate.getDate());
                patron.balance = -patron.currentBook.daysOverDue * this.dailyFine;
                return collector + -patron.balance;
        }, 0);
    }

Here is my Book class where dueDate is set and daysOverDue is calculated: 

set out(value) {
        this._out = value;
        if (value) {
            let today = new Date();
            today.setDate(today.getDate() - 14);
            this.dueDate = today;
        } else {
            this.dueDate = null;
        }
    }
get daysOverDue() {
        let today = new Date();
        let daysOverDue = today.getDate() - this.dueDate.getDate();
        return daysOverDue
    }

ASIDE: What's the difference between

this.dueDate = today.setDate(today.getDate() - 14);

and 

today.setDate(today.getDate() - 14);
this.dueDate = today;

1 Answer

Travis Alstrand
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STAFF
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Travis Alstrand
Treehouse Teacher
Travis Alstrand
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Travis Alstrand
Treehouse Teacher

I found this page which shows an example of using getDate and setDate about halfway down and subtracting days from them. I'm not exactly sure why you're getting a negative number back, if the date it has is less than 14 would it go negative and not loop through the end of the previous month?

I hope this is helpful, if not please let me know!

Travis Alstrand
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Travis Alstrand
Treehouse Teacher
Travis Alstrand
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Travis Alstrand
Treehouse Teacher

If you have a GitHub repo that you can share the link to, it'd be easier to play with it and see if we can come up with a solution. But I'm unfortunately not 100% sure why it's doing that to you, my apologies.