Validation date and number through regular expression

Validation of number through regular expression:

function validateNumber( f ) {
        var regex = new RegExp();
        //regex = /^\d+$/;
        regex = /(^-?\d\d*\.\d*$)|(^-?\d\d*$)|(^-?\.\d\d*$)/
        if ( regex.test( f.value ) ) {
                return;
        } else {
                alert("Please enter a number value");
                f.value = "";
                f.focus();
                return;
        }
}

Validation of date through regular expression:

function CheckDate(dateV)
{
        var dateStr = dateV.value;
        if(dateStr==""){
                return;
        }
        if(dateStr=="tbd" || dateStr=="TBD"){
                return;
        }
        isValidDate(dateV, dateStr);
}

function isValidDate(dateV, dateStr)
{
        var datePat = /^(\d{1,2})(\/|-)(\d{1,2})\2(\d{2}|\d{4})$/;
        var matchArray = dateStr.match(datePat);  
        if (matchArray == null) {
                alert("Date is not in a valid format.")
                dateV.focus();
                return;
        }
        month = matchArray[1]; // parse date into variables
        day = matchArray[3];
        year = matchArray[4];
        if (month < 1 || month > 12) {  
                alert("Month must be between 1 and 12.");
                dateV.focus();
                return;
        }
        if (day < 1 || day > 31) {
                        alert("Day must be between 1 and 31.");
                        dateV.focus();
                return;
        }
        if ((month==4 || month==6 || month==9 || month==11) && day==31) {
                alert("Month "+month+" doesn't have 31 days!");
                dateV.focus();
                return;
        }
        if (month == 2) {
                var isleap = (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
                if (day>29 || (day==29 && !isleap)) {
                        alert("February " + year + " doesn't have " + day + " days!");
                        dateV.focus();
                        return false;
                }
        }
        return;
}