vowela.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function countVowel(str){
            if (str==""||str==null) {
                alert("enter string"+"<br>"+"dont keep blank")
            }
            else 
            var count = str.trim().match(/[aeiou]/gi).length
           //used regex
            return count
        }

        var string = prompt(" enter a string ")
          var result = countVowel(string)
          document.write(string+" has no of vowels = "+result)
    </script>   
    
</body>
</html>