x日前的な

timeago.js

'use strict';

/*
 * JavaScript Pretty Date
 * Copyright (c) 2011 John Resig (ejohn.org)
 * Licensed under the MIT and GPL licenses.
 *
 * @original http://ejohn.org/blog/javascript-pretty-date/
 */
Util || (Util = {});
Util.date = (function() {

  function format(mstime) {
    var date = new Date(mstime);
    return date.getMonth()+1 + '月 ' + date.getDate() + '日';
  }

  return {
    pretty: function(time) {

      var mstime   = Date.parse(time),
          diff     = ((Date.now() - mstime) / 1000),
          day_diff = Math.floor(diff / 86400);

      if (isNaN(day_diff) || day_diff < 0 || day_diff >= 31) {
        return format(mstime);
      }

      return day_diff === 0 && (
             diff < 60      && Math.floor(diff) + '秒前' ||
               diff < 120     && '1分前' ||
               diff < 3600    && Math.floor(diff / 60) + '分前' ||
               diff < 7200    && '1時間前' ||
               diff < 86400   && Math.floor(diff / 3600) + '時間前'
             ) ||
             day_diff === 1 && '昨日' ||
             day_diff < 7   && day_diff + '日前' ||
             day_diff < 31  && Math.ceil(day_diff / 7) + '週間前';
    }
  };
})();