w2

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Program2</title>
</head>
<body>
    <form onsubmit="return valid()">
        Username(in DAADDAADDD):<input type="text" id="req1">
        <input type="submit" value="submit">
    </form>
    <script>
        function valid(){
            var usn=document.getElementById("req1").value;
            alert(usn);
            if(isCorrect(usn)){
                return false;
            }
            return true;
        }
        function isCorrect(elem1){
            expusn=/[0-4]{1}[A-Z]{2}[0-4]{2}[A-Z]{2}[0-9]{3}$/;
            if(elem1.length==0){
                alert("no usn is entered");
                elem1.focus();
                return false;
            }
            else if(!elem1.match(expusn)){
                alert("the usn is not in DAADDAADDD format");
                elem1.focus();
                return false;
            }
            alert("yes the usn entered is correct");
            return true;

        }
    </script>
</body>
</html>