One-Time Password Generation

<html>
<head>
    <title>One-Time Password</title>
    <script type = "text/javascript">
        function generateOTP(limit){
            var symbols = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
            var OTP = '';
            for(var i = 0; i < limit; i++)
                OTP += symbols.charAt((Math.random()*1000)%symbols.length)
            return(OTP);
        }
    </script>
</head>
<body>
    <form name = "OTP">
        Size of OTP: <input type = "text" name = "textarea" value ="8" size = "1"/>
        <input type = "submit" value ="Generate OTP" onClick = "alert('OTP is '+generateOTP(OTP.textarea.value))" />
    </form>
</html>