Date validation method

isValidDate.js

/**
 * takes an input element and validates its value as a date by converting
 * to a date object and then back to a string. Defaults to month-day-year order
 *
 * @param {HTMLElement} dateField The HTML input element to validate
 * @param {Boolean} [isDMY] Is the value in day-month-year order? Optional
 * @return {Boolean} is valid
 */
function isValidDate(dateField, isDMY) {
    var strDate = dateField.value,
        dateRegex = /(\d{1,2})[\-\s\/\.](\d{1,2})[\-\s\/\.](\d{4})/,
        dateArray,
        day,
        month,
        year,
        testDate;

    // test strDate against dateRegex and return an array with matched values
    dateArray = strDate.match(dateRegex);
    if (!dateArray) {
        // date doesn't match the regular expression so not valid
        return false;
    }

    // dateArray now contains an array with the year, month and day.
    if (!isDMY) { // US style
        day = +dateArray[2];  // using '+' sign to convert from str to number
        month = +dateArray[1];
        year = +dateArray[3];
    } else {
        day = +dateArray[1];
        month = +dateArray[2];
        year = +dateArray[3];
    }

    // create a new date object
    testDate = new Date(year, month - 1, day);

    // see if the date object's year, month, and day match our strings
    if (testDate.getFullYear() !== year) {
        return false;
    }
    if (testDate.getMonth() + 1 !== month) {
        return false;
    }
    if (testDate.getDate() !== day) {
        return false;
    }

    // if we passed these tests, we have a valid date
    return true;
}