timeAgo.js

//@flow

const templates = {
  prefix: "",
  sn: ' and %d seconds',
  suffix: " ago",
  seconds: "less than a minute",
  minute: "about a minute",
  minutes: "%d minutes",
  hour: "about an hour",
  hours: "about %d hours",
  day: "a day",
  days: "%d days",
  month: "about a month",
  months: "%d months",
  year: "about a year",
  years: "%d years"
}

function template (t, n) {
  return templates[t] && templates[t].replace(/%d/i, Math.abs(Math.round(n)));
}

export default function timeAgo(sourceTime) {
  if (!sourceTime)
    return;
  let time = sourceTime
  time = time.replace(/\.\d+/, ""); // remove milliseconds
  
  time = time.replace(/-/, "/").replace(/-/, "/");
  time = time.replace(/T/, " ").replace(/Z/, " UTC");
  time = time.replace(/([\+\-]\d\d)\:?(\d\d)/, " $1$2"); // -04:00 -> -0400
  time = new Date(time * 1000 || time);
  
  var now = new Date();
  var seconds = ((now.getTime() - time) * .001) >> 0;
  var minutes = seconds / 60;
  var hours = minutes / 60;
  var days = hours / 24;
  var years = days / 365;
  const sn = seconds % 60 === 0
    ? ''
    : template('sn', seconds % 60)
  return templates.prefix + (
    seconds < 45 && template('seconds', seconds) ||
    seconds < 90 && template('minute', 1) || (
    minutes < 45 && template('minutes', minutes) ||
    minutes < 90 && template('hour', 1) ||
    hours < 24 && template('hours', hours) ||
    hours < 42 && template('day', 1) ||
    days < 30 && template('days', days) ||
    days < 45 && template('month', 1) ||
    days < 365 && template('months', days / 30) ||
    years < 1.5 && template('year', 1) ||
      template('years', years)) + sn
  ) + templates.suffix;
}