var myDate = StringToDate('20/4/2011','dd/m/yyyy');
var actualDate;
if ( myDate != '' ) actualDate = new Date(myDate);

var MonthNames = ["January","February","March","April","May","June","July",
    "August","September","October","November","December"];
var DayNames = [ "Sunday","Monday","Tueday","Wednesday","Thursday","Friday","Saturday" ];
var ShortMths = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
var ShortDays = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];

function StringToDate(sDate, sFormat, cutOff) {
    // Input: a date value as a string, it's format as a string e.g. 'dd-mmm-yy'
    // Optional: a cutoff (integer) for 2 digit years.
    // If no 'd' appears in the format string then the 1st of the month is assumed.
    // If the year is 20 and the cut-off is 30 then the value will be converted to 2020;
    // if the year is 40 then this will be converted to 1940.
    // If no cut-off is supplied then '20' will be pre-pended to the year (YY).
    // Output: a string in the format 'YYYY/MM/DD' or ''
    // Will not attempt to convert certain combinations e.g. DMM, MDD, DDM
    var sParsed, fndSingle;          // sParsed will be constructed in the format 'YYYY/MM/DD'
    sDate = sDate.toString().toUpperCase();
    sFormat = sFormat.toUpperCase();
   
    if (sFormat.search(/MMMM|MMM/) + 1) {      // replace Mar/March with 03, etc.
        sDate = sDate.replace(new RegExp('(' + ShortMths.join('|') + ')[A-Z]*', 'gi'), function(m){
            var i = ShortMths.indexOf(m.charAt(0).toUpperCase() + m.substr(1, 2).toLowerCase()) + 1;
            return ((i < 10) ? "0" + i : "" + i).toString();
        });
        sFormat = sFormat.replace(/MMMM|MMM/g, 'MM');
    }
    if (sFormat.search(/DDDD|DDD/) + 1) {      // replace Tue/Tuesday, etc. with ''
        sDate = sDate.replace(new RegExp('(' + ShortDays.join('|') + ')[A-Z]*', 'gi'), '');
        sFormat = sFormat.replace(/DDDD|DDD/g, '');
    }
    sDate = sDate.replace(/(^|\D)(\d)(?=\D|$)/g, function($0, $1, $2){   // single digits 2 with 02
        return $1 + '0' + $2;
    });
    sFormat = sFormat.replace(/(^|[^DMY])(D|M)(?=[^DMY]|$)/g, function($0, $1, $2){
        return $1 + $2 + $2;      // replace D or M with DD and MM
    });
    fndSingle = sFormat.search(/(^|[^D])D([^D]|$)|(^|[^M])M([^M]|$)/)+1;   // are there still single Ds or Ms?
    if ( fndSingle ) return '';      // do not attempt to parse, for example, 'DMM'
    sFormat = sFormat.replace(/(^|[^Y])(YY)(?=[^Y]|$)/g, function($0, $1, $2, index){
        var tempDate = sDate.substr(0, index + 1);
        tempDate += (cutOff) ? ((parseInt(sDate.substr(index + 1, 2)) > cutOff) ? '19' : '20') : '20';
        tempDate += sDate.substr(index + 1);
        sDate = tempDate;
        return $1 + $2 + $2;
    });
    sParsed = ('YYYY/MM/DD').replace(/YYYY|MM|DD/g, function(m){
        return (sFormat.indexOf(m) + 1) ? sDate.substr(sFormat.indexOf(m), m.length) : '';
    });
    if (sParsed.charAt(0) == '/') {    // if no year specified, assume the current year
        sParsed = (new Date().getFullYear()) + sParsed;
    }
    if (sParsed.charAt(sParsed.length - 1) == '/') { // if no date, assume the 1st of the month
        sParsed += '01';
    }
    return ( sParsed.length == 10 ) ? sParsed : '';   // should end up with 10 characters..
}