js 时间字符串 格式化

Date.prototype.format = function(formatter)
{
    if(!formatter || formatter == "")
    {
        formatter = "yyyy-MM-dd";
    }
    var year = this.getYear().toString();
    var month = (this.getMonth() + 1).toString();
    var day = this.getDate().toString();
    var yearMarker = formatter.replace(/[^y|Y]/g,'');
    if(yearMarker.length == 2)
    {
        year = year.substring(2,4);
    }   
    var monthMarker = formatter.replace(/[^m|M]/g,'');
    if(monthMarker.length > 1)
    {
        if(month.length == 1)
        {
            month = "0" + month;
        }
    }   
    var dayMarker = formatter.replace(/[^d]/g,'');
    if(dayMarker.length > 1)
    {
        if(day.length == 1)
        {
            day = "0" + day;
        }
    }   
    return formatter.replace(yearMarker,year).replace(monthMarker,month).replace(dayMarker,day);   
}

Date.parseString = function(dateString,formatter)
{
    var today = new Date();
    if(!dateString || dateString == "")
    {
        return today;
    }
    if(!formatter || formatter == "")
    {
        formatter = "yyyy-MM-dd";
    } 
    var yearMarker = formatter.replace(/[^y|Y]/g,'');  
    var monthMarker = formatter.replace(/[^m|M]/g,'');  
    var dayMarker = formatter.replace(/[^d]/g,'');
    var yearPosition = formatter.indexOf(yearMarker);
    var yearLength = yearMarker.length;
    var year =  dateString.substring(yearPosition ,yearPosition + yearLength) * 1;
    if( yearLength == 2)
    {
        if(year < 50 )
        {
            year += 2000;
        }
        else
        {
            year += 1900;
        }
    }
    var monthPosition = formatter.indexOf(monthMarker);
    var month = dateString.substring(monthPosition,monthPosition + monthMarker.length) * 1 - 1;
    var dayPosition = formatter.indexOf(dayMarker);
    var day = dateString.substring( dayPosition,dayPosition + dayMarker.length )* 1;
    return new Date(year,month,day);
}