Validate a date string #JavaScript

isValidDate.js

// Validates whether the given date string is in MM/DD/YYYY format, and if it is a valid date.
var isValidDate = function (dateString) {
    // Validate the date string for the format via regular expressions. In this case it is MM/DD/YYYY
    var dateRegEx = new RegExp('^(0?[1-9]|1[012])/(0?[1-9]|[12][0-9]|3[01])/((19|20)\\d\\d)$' ); // Date Format: MM/DD/YYYY
    if (dateRegEx.test(dateString)) {
        var dateTokens = dateString.split('/' );
        var timestamp = Date.parse(dateString);
        // Parsing the date in javascript into the no. of milliseconds since Jan 1, 1970 is
        // an added line of defense to check whether the date format is correct.
        if (!isNaN(timestamp)) {
            // Date.parse() parses a date string even if it is logically incorrect.
            // e.g. When you parse Feb 30, 2013, it gives you milliseconds till Mar 2, 2013 without any errors.
            // Here comes the one-to-one checking of the actual month, day and year literals.
            var date = new Date(dateString);
            if (parseInt(date.getMonth(), 10) + 1 === parseInt(dateTokens[0], 10)
                && parseInt(date.getDate(), 10) === parseInt(dateTokens[1], 10)
                && parseInt(date.getYear(), 10) === parseInt(dateTokens[2], 10)) {
                return true ;
            }
        }
    }
    return false;
};