Validación de fecha con JavaScript

checkDate.js

//------------------------------DATE CHECK-------------------------------------

// Returns if a given string date is valid. Months, days and years have the normal 
// numeration starting from 1
// Valid formats for the string date: dd-mm-yy / dd/mm/yy / dd mm yy
function checkDate(dateString){
    var dateStringParsed = parseDate();
    
    if(dateStringParsed === null){
        return false;
    }

    var day = dateStringParsed.day;
    var month = parseInt(dateStringParsed.month);
    month--; //Change the month to index
    var year = dateStringParsed.year;

    return isValidDate() && dateNotAhead();

    // Parse date string from input field
    // Takes dateString as variable
    function parseDate() {
        var regEx = new RegExp("[-/\\s]", "g");
        dateString = dateString.replace(regEx, "/");
        dateString = dateString.split("/");

        if(dateString.length !== 3){
            return null;
        }
        
        return {day : dateString[0],
                month : dateString[1],
                year : dateString[2]};
    }

    //Checks if day, month and year are a real date
    function isValidDate(){
        var month_short_names = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
            'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
        var dateString = month_short_names[month] + " " +
                day.toString() + " " +
                year.toString();
        console.log(dateString);
        return !isNaN(Date.parse(dateString));
    }

    //Checks that the introduced date (day, month and year variables)
    //isn't ahead
    function dateNotAhead(){
        var currentDateMs = Date.parse(new Date());
        var providedDateMs = Date.parse(new Date(year, month, day));

        return currentDateMs >= providedDateMs;
    }
}