Convert string to date

[AndrewGSW]

If you supply the following function with a date as a string '20/4/2011' and a corresponding format descriptor 'dd/m/yyyy' it will return another string in the format '2011/04/20'. This returned value can be used to create a valid Date variable.

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

You can also supply a third argument to handle two digit years. (Note that it will not handle confusing formats such as 'ddm', but will correctly handle the variable lengths of month and day names.)
It requires ShortMths and ShortDays (but I've posted MonthNames and DayNames as well):

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..
}

I have also used it to correctly sort tables by date columns. Andy.

[Kor]

To avoid confusion and possible errors, usually the problem is solved otherwise. The developer should simply used 3 different elements (text boxes or even better related select boxes) for year, month and date. No need for further intricate conversions, presumptions, validations, and so on. The KISS principle, you know...

[AndrewGSW]

Originally Posted by Kor

To avoid confusion and possible errors, usually the problem is solved otherwise. The developer should simply used 3 different elements (text boxes or even better related select boxes) for year, month and date. No need for further intricate conversions, presumptions, validations, and so on. The KISS principle, you know...

I agree, and wouldn't use my function for form validation of a date. I built it because I wanted to sort a column of dates in a table (and wasn't happy with the methods I found elsewhere).