第一种:

/** 
 * 时间对象的格式化; 
 */  
Date.prototype.format = function(format) {  
    /* 
     * eg:format="YYYY-MM-dd hh:mm:ss"; 
     */  
    var o = {  
        "M+" :this.getMonth() + 1, // month  
        "d+" :this.getDate(), // day  
        "h+" :this.getHours(), // hour  
        "m+" :this.getMinutes(), // minute  
        "s+" :this.getSeconds(), // second  
        "q+" :Math.floor((this.getMonth() + 3) / 3), // quarter  
        "S" :this.getMilliseconds()  
    // millisecond  
    }  
  
    if (/(y+)/.test(format)) {  
        format = format.replace(RegExp.$1, (this.getFullYear() + "")  
                .substr(4 - RegExp.$1.length));  
    }  
  
    for ( var k in o) {  
        if (new RegExp("(" + k + ")").test(format)) {  
            format = format.replace(RegExp.$1, RegExp.$1.length == 1 ? o[k]  
                    : ("00" + o[k]).substr(("" + o[k]).length));  
        }  
    }  
    return format;  
}  

var   now = new Date().format("yyyy-MM-dd hh:mm:ss"); 

第二种：

Date.protoType.format = function(mask) {  
    var d = this;  
  
    var zeroize = function (value, length) {  
  
        if (!length) length = 2;  
  
        value = String(value);  
  
        for (var i = 0, zeros = ''; i < (length - value.length); i++) {  
  
            zeros += '0';  
  
        }  
  
        return zeros + value;  
  
    };  
  
    return mask.replace(/"[^"]*"|'[^']*'|\b(?:d{1,4}|m{1,4}|yy(?:yy)?|([hHMstT])\1?|[lLZ])\b/g, function($0) {  
  
        switch($0) {  
  
            case 'd':   return d.getDate();  
  
            case 'dd':  return zeroize(d.getDate());  
  
            case 'ddd': return ['Sun','Mon','Tue','Wed','Thr','Fri','Sat'][d.getDay()];  
  
            case 'dddd':return ['Sunday','Monday','Tuesday','Wednesday','Thursday','Friday','Saturday'][d.getDay()];  
  
            case 'M':   return d.getMonth() + 1;  
  
            case 'MM':  return zeroize(d.getMonth() + 1);  
  
            case 'MMM': return ['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'][d.getMonth()];  
  
            case 'MMMM':return ['January','February','March','April','May','June','July','August','September','October','November','December'][d.getMonth()];  
  
            case 'yy':  return String(d.getFullYear()).substr(2);  
  
            case 'yyyy':return d.getFullYear();  
  
            case 'h':   return d.getHours() % 12 || 12;  
  
            case 'hh':  return zeroize(d.getHours() % 12 || 12);  
  
            case 'H':   return d.getHours();  
  
            case 'HH':  return zeroize(d.getHours());  
  
            case 'm':   return d.getMinutes();  
  
            case 'mm':  return zeroize(d.getMinutes());  
  
            case 's':   return d.getSeconds();  
  
            case 'ss':  return zeroize(d.getSeconds());  
  
            case 'l':   return zeroize(d.getMilliseconds(), 3);  
  
            case 'L':   var m = d.getMilliseconds();  
  
                    if (m > 99) m = Math.round(m / 10);  
  
                    return zeroize(m);  
  
            case 'tt':  return d.getHours() < 12 ? 'am' : 'pm';  
  
            case 'TT':  return d.getHours() < 12 ? 'AM' : 'PM';  
  
            case 'Z':   return d.toUTCString().match(/[A-Z]+$/);  
  
            // Return quoted strings with the surrounding quotes removed  
  
            default:    return $0.substr(1, $0.length - 2);  
  
        }  
  
    });  
};  

转载自：http://baalwolf.iteye.com/blog/1124649