Hi nauna,
Add JScript File from Add New Item context menu in your project and writhe the javascript code in that.
Add the JScript File reference in the page.
Check this example. Now please take its reference and correct your code.
HTML
<head>
<title></title>
<script src="JScript.js" type="text/javascript"></script>
</head>
<body>
<div>
Alphanumeric value:
<input type="text" id="text1" onkeypress="return IsAlphaNumeric(event);" ondrop="return false;"
onpaste="return false;" />
<span id="error" style="color: Red; display: none">* Special Characters not allowed.</span>
</div>
</body>
</html>
JScript.js
var specialKeys = new Array();
specialKeys.push(8); //Backspace
specialKeys.push(9); //Tab
specialKeys.push(46); //Delete
specialKeys.push(36); //Home
specialKeys.push(35); //End
specialKeys.push(37); //Left
specialKeys.push(39); //Right
function IsAlphaNumeric(e) {
var keyCode = e.keyCode == 0 ? e.charCode : e.keyCode;
var ret = ((keyCode >= 48 && keyCode <= 57) || (keyCode >= 65 && keyCode <= 90) || (keyCode >= 97 && keyCode <= 122) || (specialKeys.indexOf(e.keyCode) != -1 && e.charCode != e.keyCode));
document.getElementById("error").style.display = ret ? "none" : "inline";
return ret;
}
Screenshot
