封装一个处理日期格式的函数

/**
 * 参数归一化
 * 格式化一个日期
 * @param {Date} date
 */
function formatDate(date, formatter, isPad = false) {
  formatter = _formatNormalize(formatter);
  function _pad(value, length) {
    if (isPad) {
      return (value + "").padStart(length, "0");
    } else {
      return value.toString();
    }
  }
  const dateInfo = {
    year: date.getFullYear(),
    month: date.getMonth() + 1,
    day: date.getDate(),
    hour: date.getHours(),
    minute: date.getMinutes(),
    second: date.getSeconds(),
  };
  dateInfo.YYYY = _pad(dateInfo.year, 4);
  dateInfo.MM = _pad(dateInfo.month, 2);
  dateInfo.DD = _pad(dateInfo.day, 2);
  dateInfo.HH = _pad(dateInfo.hour, 2);
  dateInfo.mm = _pad(dateInfo.minute, 2);
  dateInfo.ss = _pad(dateInfo.second, 2);
  return formatter(dateInfo);
}

function _formatNormalize(formatter) {
  if (typeof formatter === "function") {
    return formatter;
  }
  if (typeof formatter !== "string") {
    throw new Error("formatter must be a function or a string");
  }
  if (formatter === "date") {
    formatter = "YYYY-MM-DD";
  } else if (formatter === "datetime") {
    formatter = "YYYY-MM-DD HH:mm:ss";
  }
  return (dateInfo) => {
    const { YYYY, MM, DD, HH, mm, ss } = dateInfo;
    return formatter
      .replace(/YYYY/g, YYYY)
      .replace(/MM/g, MM)
      .replace(/DD/g, DD)
      .replace(/HH/g, HH)
      .replace(/mm/g, mm)
      .replace(/ss/g, ss);
  };
}

console.log(formatDate(new Date(1218197288000), "YYYY-MM-DD HH:mm:ss", true)); // 2008-08-08 20:08:08