Next Day

Problem Statement

In the given task, the objective is to extend the functionality of JavaScript date objects so that you can utilize a method named nextDay() on any date object. The method should return the day following the date of the given object in a string format adhering to the standard "YYYY-MM-DD". This enhancement allows programmers to directly get the next day without performing manual calculations or adjustments based on month lengths, leap years, etc., making it a simpler and more efficient process.

Examples

Example 1

Input:

date = "2014-06-20"

Output:

"2014-06-21"

Explanation:

const date = new Date("2014-06-20");
date.nextDay(); // "2014-06-21"

Example 2

Input:

date = "2017-10-31"

Output:

"2017-11-01"

Explanation:

The day after 2017-10-31 is 2017-11-01.

Constraints

• new Date(date) is a valid date object.

Approach and Intuition

To implement nextDay() for all JavaScript Date objects, we extend the prototype of the Date class. JavaScript's Date object internally handles leap years, month rollovers, and year transitions when the day of the month is increased beyond the valid limit for a given month.

Here’s the step-by-step breakdown:

1. Access the Date Value Use this.getDate() to retrieve the day of the month.

2. Increment by One Day Call this.setDate(this.getDate() + 1) which updates the date to the next day. If the update exceeds the month’s last day, JavaScript’s engine automatically rolls the date to the next month or year.

3. Format the New Date Use:

   • this.getFullYear() for the year.
   • this.getMonth() + 1 (since months are 0-indexed).
   • this.getDate() for the day of the month. Then format it as "YYYY-MM-DD" using padStart(2, '0') for month and day to ensure two-digit output.

4. Return the Result Return the formatted date string as the result of nextDay().

Solutions

Date.prototype.incrementDay = function() {
    const monthDays = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
    const currentYear = this.getFullYear();
    const currentMonth = this.getMonth();    
    const currentDay = this.getDate();      

    const leapYearCheck = (currentYear % 4 === 0 && currentYear % 100 !== 0) || (currentYear % 400 === 0);
    if (leapYearCheck) {
        monthDays[1] = 29; // Update February days for leap year
    }

    const daysInCurrentMonth = monthDays[currentMonth];
    
    let futureYear = currentYear;
    let futureMonth = currentMonth;
    let upcomingDay = currentDay + 1;

    // Adjust date when overflowing the current month
    if (upcomingDay > daysInCurrentMonth) {
        upcomingDay = 1;
        futureMonth += 1;
        if (futureMonth > 11) {
            futureMonth = 0;
            futureYear += 1;
        }
    }

    // Construct and return the next day's date in YYYY-MM-DD format
    const nextDate = ``{futureYear}-`{String(futureMonth + 1).padStart(2, '0')}-${String(upcomingDay).padStart(2, '0')}`;
    return nextDate;
};