JavaScript for Validation of Date

<script type="text/javascript">

    function checkdate(input) {

        var validformat = /(?:0[1-9]|1[0-2])\/(?:0[1-9]|[12][0-9]|3[01])\/(?:19|20\d{2})/;  //Basic check for format validity

        var returnval = false

        if (!validformat.test(input.value))

            alert("Please insert a valid date")

        else { //Detailed check for valid date ranges

            var monthfield = input.value.split("/")[0]

            var dayfield = input.value.split("/")[1]

            var yearfield = input.value.split("/")[2]

            var dayobj = new Date(yearfield, monthfield - 1, dayfield)

           

            if ((dayobj.getMonth() + 1 != monthfield) || (dayobj.getDate() != dayfield) || (dayobj.getFullYear() != yearfield))

                alert("Invalid Date Please correct and submit again.")

            else

                returnval = true

        }

        if (returnval == false) input.select()

        return returnval

    }

</script>