As the title says, i am, trying to disable textbox when i open the file

<form name='registration' action="registration.php" method="post" onSubmit="return formValidation();">

    <table>

        <tr>

            <td>FirstName:</td>     

            <td><input type = "Text" name = "firstname" id="1"></p></td>

        </tr>

    </table>

</form>

and I try ti disable it using the following javascript code:

function formValidation() {

    var fn = document.registration.firstname;

    if(fname_validation(fn)) {}

    document.getElementById("1").disabled = true;

}



function fname_validation(fn) {

    var fn_len = fn.value.length;

    var fn_char = /^[A-Za-z]+$/;

    if (fn_len == 0) {

        alert("first name cannot empty");

        return false;

    }

    if (!fn.value.match(fn_char)) {

        alert("first name must enter alphabet only");

        return false;

    } else {

        return true;

    }

}

Why the text box still does not disable?