How many days are left Calculator

Features:

1. Target Date Input: Users can select a future or past target date, and the calculator will show how many days are left or have passed.
2. Custom Start Date: Users can optionally select a custom start date from which to calculate the number of days until the target date.
3. Dynamic Output: If the target date is in the past, the calculator will tell the user how many days have passed since that date. If it’s today, it will inform them that today is the target date.
4. Validation: The code checks for valid date inputs and informs the user if the input is invalid.

How It Works:

1. The user selects a target date and, optionally, a custom start date.
2. The script calculates the difference in days between the two dates using JavaScript’s Date object and displays the result.
3. The result is shown dynamically, indicating whether the date is in the future, past, or today.