Portuguese NIF validation

HTML

<form>
    <input type="text" id="NIF"/>
    <input type="submit" id="submit" value="submeter"/>
</form>
<div id="msg"></div>

JavaScript

function validateNIF(nif){
    if(nif.length == 9){
        added = ((nif[7]*2)+(nif[6]*3)+(nif[5]*4)+(nif[4]*5)+(nif[3]*6)+(nif[2]*7)+(nif[1]*8)+(nif[0]*9));
        mod = added % 11;
        alert(mod);
        if(mod == 0 || mod == 1){
            control = 0;
        } else {
             control = 11 - mod;   
        }
        
        if(nif[8] == control){
            return true;
        } else {
             return false;  
        }
    } else {
        return false;
    }
}

$('#submit').click(function(){
    if(validateNIF($("#NIF").val())){
        $('#msg').html('V&aacute;lido');
    } else {
        $('#msg').html('Inv&aacute;lido');   
    }
    event.preventDefault();
});