Textbox validation for special characters

Write this javascript code inside "HEAD" -> "SCRIPT" tag

function validtForSpclChar()

{

var chkStr = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

var chkTxt = form1.TextBox1.value;

var allValid = true;

for (i = 0; i <>

{

ch = chkTxt.charAt(i);

for (j = 0; j <>

if (ch == chkStr.charAt(j))

break;

if (j == chkStr.length)

{

allValid = false;

break;

}

}

if (!allValid)

{

alert("Enter only letter and numeric characters in the \"TextBox\" field.");

form1.TextBox1.focus();

return (false);

}

}

call this function in form's onsubmit event

form id="form1" runat="server" onsubmit="return validtForSpclChar(this)"