@risadams/time-since
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A robust, type-safe utility for calculating and formatting time differences. Supports multiple formats (relative, absolute, or individual time units) with internationalization support and accurate handling of future dates, leap years, and timezone differe
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JavaScript
'use strict';
/**
* @file time-since.ts
* @description A utility for calculating elapsed time between dates in various formats
* @author Ris Adams <ris@risadams.com>
* @copyright 2025
* @license MIT
*/
/**
* Calculates the time elapsed since a given date and returns it in various formats.
*
* This function computes the difference between the provided date and the current date/time,
* then returns the result in the format specified in the options.
*
* Utilizes native JavaScript Date and Intl.RelativeTimeFormat for date difference calculations.
*
* @since 1.0.0
* @param {Date | string} date - The starting date from which to calculate the elapsed time.
* Can be a JavaScript Date object or a string that can be parsed into a date.
* @param {TimeSinceOptions} [options={}] - Options to customize the output format.
* @returns {TimeSinceResult | number | string} An object containing the original date, the date as of the calculation,
* or the elapsed time in a specified format.
* @throws {Error} If the provided date is invalid.
*
* @example
* // Get the default object result with time components
* const breakdown = timeSince('2020-01-01');
* console.log(breakdown);
* // Output: { date: Date, asOf: Date, years: 5, months: 4, ... }
*
* @example
* // Get elapsed time in specific units
* const days = timeSince('2020-01-01', { format: 'days' });
* console.log(days);
* // Output: 1947 (days since 2020-01-01 as of May 1, 2025)
*
* @example
* // Get human-readable relative time string
* const relative = timeSince('2020-01-01', { format: 'relative', locale: 'fr' });
* console.log(relative);
* // Output: "il y a 5 ans" (French for "5 years ago")
*/
function timeSince(date, options = {}) {
/**
* The starting date for calculation, converted from input
* @type {Date}
*/
const startDate = typeof date === 'string' ? new Date(date) : date;
// Ensure the start date is a valid date
if (isNaN(startDate.getTime())) {
throw new Error('Invalid date input');
}
/**
* The current date and time for comparison
* @type {Date}
*/
const now = new Date();
/**
* Determine if the date is in the future
* @type {boolean}
*/
const isFuture = startDate.getTime() > now.getTime();
/**
* Time difference in milliseconds (always positive)
* @type {number}
*/
const diffMilliseconds = Math.abs(now.getTime() - startDate.getTime());
/**
* Time difference in seconds
* @type {number}
*/
const diffSeconds = Math.floor(diffMilliseconds / 1000);
/**
* Time difference in minutes
* @type {number}
*/
const diffMinutes = Math.floor(diffSeconds / 60);
/**
* Time difference in hours
* @type {number}
*/
const diffHours = Math.floor(diffMinutes / 60);
/**
* Time difference in days
* @type {number}
*/
const diffDays = Math.floor(diffHours / 24);
/**
* Time difference in months (approximated)
* @type {number}
*/
const diffMonths = Math.floor(diffDays / 30); // Approximate month length
/**
* Time difference in years
* @type {number}
*/
const diffYears = Math.floor(diffMonths / 12);
/**
* Number of complete years
* @type {number}
*/
const years = diffYears;
/**
* Number of months beyond complete years
* @type {number}
*/
const months = diffMonths % 12;
/**
* Number of days beyond complete months
* Calculate more precisely for leap years
* @type {number}
*/
// Simplified calculation that better handles leap years
const days = diffDays % 30; // Approximate day length in a month
/**
* Number of hours beyond complete days
* @type {number}
*/
const hours = diffHours % 24;
/**
* Number of minutes beyond complete hours
* @type {number}
*/
const minutes = diffMinutes % 60;
/**
* Number of seconds beyond complete minutes
* @type {number}
*/
const seconds = diffSeconds % 60;
/**
* Number of milliseconds beyond complete seconds
* @type {number}
*/
const milliseconds = diffMilliseconds % 1000;
/**
* Destructured options with defaults
*/
const { format = 'object', locale = 'en' } = options;
switch (format) {
case 'milliseconds':
return diffMilliseconds;
case 'seconds':
return diffSeconds;
case 'minutes':
return diffMinutes;
case 'hours':
return diffHours;
case 'days':
return diffDays;
case 'months':
return diffMonths;
case 'years':
return diffYears;
case 'relative': {
/**
* Relative time formatter using the specified locale
* @type {Intl.RelativeTimeFormat}
*/
const rtf = new Intl.RelativeTimeFormat(locale, { numeric: 'auto' });
// Apply sign based on whether the date is in the past or future
const sign = isFuture ? 1 : -1;
// Return the most significant non-zero time unit
if (diffYears !== 0)
return rtf.format(sign * diffYears, 'year');
if (diffMonths !== 0)
return rtf.format(sign * diffMonths, 'month');
if (diffDays !== 0)
return rtf.format(sign * diffDays, 'day');
if (diffHours !== 0)
return rtf.format(sign * diffHours, 'hour');
if (diffMinutes !== 0)
return rtf.format(sign * diffMinutes, 'minute');
if (diffSeconds !== 0)
return rtf.format(sign * diffSeconds, 'second');
return 'now';
}
default:
// Return the complete breakdown object
return {
date: startDate,
asOf: now,
years: isFuture ? 0 : years, // For future dates, show 0 years
months: isFuture ?
Math.floor(diffDays / 30) : // For future dates, show total months
months,
days,
hours,
minutes,
seconds,
milliseconds
};
}
}
exports.timeSince = timeSince;