fromNow.js

/**
 * Human readable elapsed or remaining time (example: 3 minutes ago)
 * @param  {Date|Number|String} date A Date object, timestamp or string parsable with Date.parse()
 * @return {string} Human readable elapsed or remaining time
 * @author github.com/victornpb
 */
function fromNow(date) {
    const SECOND = 1000;
    const MINUTE = 60 * SECOND;
    const HOUR = 60 * MINUTE;
    const DAY = 24 * HOUR;
    const WEEK = 7 * DAY;
    const MONTH = 30 * DAY;
    const YEAR = 365 * DAY;
    const intervals = [
        { ge: 2 * YEAR, divisor: YEAR, elapsed: '# years ago', remaining: 'in # years' },
        { ge: YEAR, divisor: YEAR, elapsed: 'last year', remaining: 'in a year' },
        { ge: 2 * MONTH, divisor: MONTH, elapsed: '# months ago', remaining: 'in # months' },
        { ge: MONTH, divisor: MONTH, elapsed: 'last month', remaining: 'in a month' },
        { ge: 2 * WEEK, divisor: WEEK, elapsed: '# weeks ago', remaining: 'in # weeks' },
        { ge: WEEK, divisor: WEEK, elapsed: 'last week', remaining: 'in a week' },
        { ge: 2 * DAY, divisor: DAY, elapsed: '# days ago', remaining: 'in # days' },
        { ge: DAY, divisor: DAY, elapsed: 'yesterday', remaining: 'tomorrow', },
        { ge: 2 * HOUR, divisor: HOUR, elapsed: '# hours ago', remaining: 'in # hours' },
        { ge: HOUR, divisor: HOUR, elapsed: 'an hour ago', remaining: 'in an hour' },
        { ge: 2 * MINUTE, divisor: MINUTE, elapsed: '# minutes ago', remaining: 'in # minutes' },
        { ge: MINUTE, divisor: MINUTE, elapsed: 'a minute ago', remaining: 'in a minute' },
        { ge: 30 * SECOND, divisor: SECOND, elapsed: '# seconds ago', remaining: 'in # seconds' },
        { ge: 0, divisor: 1, elapsed: 'just now', remaining: 'just now' },
    ];
    const diff = Date.now() - (typeof date === 'object' ? date : new Date(date)).getTime();
    const diffAbs = Math.abs(diff);
    for (const interval of intervals) {
        if (diffAbs >= interval.ge) {
            const x = Math.round(Math.abs(diff) / interval.divisor);
            const isFuture = diff < 0;
            return String(isFuture ? interval.remaining : interval.elapsed).replace('#', x);
        }
    }
}