Between Dates

This function calculates the number of days between two dates.

Function

/**
 * Calculates the number of days between two dates.
 *
 * @param {Date} startDate - The start date.
 * @param {Date} endDate - The end date.
 * @param {boolean} [inclusive=true] - Whether to include the start and end dates in the count.
 * @returns {number} The number of days between the dates, or an error message if the end date is earlier than the start date.
 */
function betweenDates(startDate, endDate, inclusive = true) {
    if (startDate > endDate) {
        throw new Error("End date cannot be earlier than the Start date.");
    }
    // Calculate the time difference in milliseconds
    const timeDifference = Math.abs(endDate - startDate);

    // Convert time difference from milliseconds to days
    const millisecondsPerDay = 1000 * 60 * 60 * 24;
    const daysDifference = Math.ceil(timeDifference / millisecondsPerDay);

    return inclusive ? daysDifference + 1 : ((daysDifference - 1) >= 0 ? daysDifference - 1 : 0);
}

Parameters

• startDate (Date): The start date.
• endDate (Date): The end date.
• inclusive (boolean, optional): Whether to include the start and end dates in the count. Defaults to true.

Returns

• number: The number of days between the dates, or an error message if the end date is earlier than the start date.

Usage

const startDate = new Date('2023-01-01');
const endDate = new Date('2023-01-10');

console.log(betweenDates(startDate, endDate)); // Output: 10
console.log(betweenDates(startDate, endDate, false)); // Output: 8

Error Handling

If the endDate is earlier than the startDate, the function will throw an error:

const startDate = new Date('2023-01-10');
const endDate = new Date('2023-01-01');

try {
    console.log(betweenDates(startDate, endDate));
} catch (error) {
    console.error(error.message); // Output: End date cannot be earlier than the Start date.
}