JavaScript-日期格式化（一）

    /**
      * 日期格式化，
      * @param date 要格式化的日期
      * @param pattern 进行格式化的模式
      *     支持的模式字母有：
      *     y:年,
      *     M:年中的月份(1-12),
      *     d:月份中的天(1-31),
      *     H:小时(0-23),
      *     h:小时(0-12),
      *     m:分(0-59),
      *     s:秒(0-59),
      *     S:毫秒(0-999),
      *     E:星期(以汉语表示),
      *     e:星期(以英文表示),
      *     A:上午/下午标识,
      *     a:AM/PM标识
      * @return
      */
    function formatDate(date,pattern){
         var d;
         if((d=parseDate(date))==null){
             return "";
         }
         if(!pattern){
             pattern = "yyyy-MM-dd";
         }
         var arrWeek = ["星期日","星期一","星期二","星期三","星期四","星期五","星期六","Sunday","Monday","Tuesday","Tuesday","Thursday","Friday","Saturday"];
         var value = new Object();
         value["y"] = parseString(date.getFullYear());
         value["M"] = parseString(date.getMonth() + 1);
         value["d"] = parseString(date.getDate());
         value["H"] = parseString(date.getHours());
         value["h"] = parseString(value["H"] > 12 ? (value["H"]-12) : value["H"]);
         value["m"] = parseString(date.getMinutes());
         value["s"] = parseString(date.getSeconds());
         value["S"] = parseString(date.getMilliseconds());
         value["E"] = arrWeek[date.getDay()];
         value["e"] = arrWeek[date.getDay() + 7];
         value["a"] = (value["H"] > 12 ? "PM" : "AM");
         value["A"] = (value["H"] > 12 ? "下午" : "上午");
         var result = "";
         var i = 0;
         var hasE = false;//是否出现过星期
         var hasAMPM = false;//是否出现过上午下午
         while(i < pattern.length){
             var c = pattern.charAt(i++);
             var lc = c;//记录本次要处理的字母,如'y'
             var tmpStr = c;//本次在处理的字母格式,如'yyyy'
             while(i < pattern.length && (c=pattern.charAt(i))==lc){
                 tmpStr += c;
                 i++;
             }
             if(value[lc]!=""&&value[lc]!=null&&value[lc]!="undefined"){
                 //本次要处理的字母是模式母
                 if((lc == "E" || lc == "e") && !hasE){
                     //星期
                     result += value[lc];
                     hasE = true;
                 } else if(lc == "E" || lc == "e") {
                     result += tmpStr;
                 } else if((lc=="a" || lc == "A")  && !hasAMPM){
                     //上下午
                     result += value[lc];
                     hasAMPM = true;
                 } else if((lc=="a" || lc == "A") ){
                     result += tmpStr;
                 } else {
                     //如果是 单个的日期，月份，小时，分，秒的字符串，不能再进行字符串的截取操作
                     if(tmpStr == "d" || tmpStr == "M" || tmpStr=="H" || tmpStr=="h" || tmpStr == "m" || tmpStr == "s"){
                         result += value[lc];
                     } else {
                         result += value[lc].fillChar(tmpStr.length);
                     }
                 }
             } else {//非模式字母，直接输出
                 result += tmpStr;
             }
         }
         return result;
     }  

测试：

var date = new Date();
document.write(formatDate(date,"yyyy-MM-dd HH:mm:ss.SSS E") + "<br>");
document.write(formatDate(date,"yyyy年MM月dd日 HH时mm分ss秒 E") + "<br>");
document.write(formatDate(date,"yyyy-M-d hh:mm:ss.SSS A E") + "<br>");
document.write(formatDate(date,"MM/dd/yy hh:mm:ss a e") + "<br>");
document.write(formatDate(date,"M/d/yyyy") + "<br>");