//字符串转换为时间戳
function getDateTimeStamp (dateStr) {
  return Date.parse(dateStr.replace(/-/gi,"/"));
}

function getDateDiff (dateStr) {
  var publishTime = getDateTimeStamp(dateStr)/1000,
    d_seconds,
    d_minutes,
    d_hours,
    d_days,
    timeNow = parseInt(new Date().getTime()/1000),
    d,
    date = new Date(publishTime*1000),
    Y = date.getFullYear(),
    M = date.getMonth() + 1,
    D = date.getDate(),
    H = date.getHours(),
    m = date.getMinutes(),
    s = date.getSeconds();
    //小于10的在前面补0
    if (M < 10) {
      M = '0' + M;
    }
    if (D < 10) {
      D = '0' + D;
    }
    if (H < 10) {
      H = '0' + H;
    }
    if (m < 10) {
      m = '0' + m;
    }
    if (s < 10) {
      s = '0' + s;
    }
  d = timeNow - publishTime;
  d_days = parseInt(d/86400);
  d_hours = parseInt(d/3600);
  d_minutes = parseInt(d/60);
  d_seconds = parseInt(d);
  if(d_days > 0 && d_days < 3){
    return d_days + '天前';
  }else if(d_days <= 0 && d_hours > 0){
    return d_hours + '小时前';
  }else if(d_hours <= 0 && d_minutes > 0){
    return d_minutes + '分钟前';
  }else if (d_seconds < 60) {
    if (d_seconds <= 0) {
      return '刚刚发表';
    }else {
      return d_seconds + '秒前';
    }
  }else if (d_days >= 3 && d_days < 30){
    return M + '-' + D + '&nbsp;' + H + ':' + m;
  }else if (d_days >= 30) {
    return Y + '-' + M + '-' + D + '&nbsp;' + H + ':' + m;
  }
}  

// 转换后的结果 
var str = getDateDiff(dateStr);
// 在控制台输出结果 
console.log(str);