JavaScript time passed string from date

Want to have time strings like "n seconds ago" or "m months ago"? Here's a short script.

export function friendlyTimePassed(targetDate) {
    let timeDifferenceMilliseconds = new Date().getTime()-targetDate.getTime();
    const ms = 1000;
    const min = 60 * ms;
    const hrs = 60 * min;
    const days = 24 * hrs;
    const week = 7 * days;
    const month = 30.41666666 * days;
    const year = days * 365;

    let diffSeconds = (timeDifferenceMilliseconds / ms).toFixed(0);
    if (diffSeconds < 1) {
        return "less then a second";
    }

    let diffMinutes = timeDifferenceMilliseconds / min;
    if (diffMinutes < 1) {
        return diffSeconds.toFixed(0) + " seconds ago";
    }

    let diffHours = timeDifferenceMilliseconds / hrs;
    if (diffHours < 1) {
        return diffMinutes.toFixed(0) + " minutes ago";
    }

    let diffDays = timeDifferenceMilliseconds / days;
    if (diffDays < 1) {
        return diffHours.toFixed(0) + " hours ago";
    }

    let diffWeeks = timeDifferenceMilliseconds / week;
    if (diffWeeks < 1) {
        return diffDays.toFixed(0) + " days ago";
    }

    let diffMonths = timeDifferenceMilliseconds / month;
    if (diffMonths < 1) {
        return diffWeeks.toFixed(0) + " weeks ago";
    }

    let diffYears = timeDifferenceMilliseconds / year;
    if (diffYears < 1) {
        return diffMonths.toFixed(0) + " months ago";
    }

    return diffYears + " years ago";
}

Feel free to use it or to make it significantly better :).