JS validador de NIF & CIF

nifcif_validador.js

//Retorna: 1 = NIF ok, 2 = CIF ok, 3 = NIE ok, -1 = NIF error, -2 = CIF error, -3 = NIE error, 0 = ??? error
function valida_nif_cif_nie(a){
    var temp = a.toUpperCase();
    var cadenadni = "TRWAGMYFPDXBNJZSQVHLCKE";
    if( temp!= '' )	{
        //si no tiene un formato valido devuelve error
        if( ( !/^[A-Z]{1}[0-9]{7}[A-Z0-9]{1}$/.test( temp ) && !/^[T]{1}[A-Z0-9]{8}$/.test( temp ) ) && !/^[0-9]{8}[A-Z]{1}$/.test( temp ) ){
            return 0;
        }
        //comprobacion de NIFs estandar
        if( /^[0-9]{8}[A-Z]{1}$/.test( temp )){
            posicion = a.substring( 8,0 ) % 23;
            letra = cadenadni.charAt( posicion );
            var letradni = temp.charAt( 8 );
            if( letra == letradni ){
                return 1;
            }else{
                return -1;
            }
        }
        //algoritmo para comprobacion de codigos tipo CIF
        suma = parseInt(a.charAt(2))+parseInt(a.charAt(4))+parseInt(a.charAt(6));
        for( i = 1; i < 8; i += 2 )		{
            temp1 = 2 * parseInt( a.charAt( i ) );
            temp1 += '';
            temp1 = temp1.substring(0,1);
            temp2 = 2 * parseInt( a.charAt( i ) );
            temp2 += '';
            temp2 = temp2.substring( 1,2 );
            if( temp2 == '' ){
                temp2 = '0';
            }
            suma += ( parseInt( temp1 ) + parseInt( temp2 ) );
        }
        suma += '';
        n = 10 - parseInt( suma.substring( suma.length-1, suma.length ) );

        //comprobacion de NIFs especiales (se calculan como CIFs)
        if( /^[KLM]{1}/.test( temp ) ){
            if( a.charAt( 8 ) == String.fromCharCode( 64 + n ) ){
                return 1;
            }else{
                return -1;
            }
        }
        //comprobacion de CIFs
        if( /^[ABCDEFGHJNPQRSUVW]{1}/.test( temp ) ){
            temp = n + '';
            if( a.charAt( 8 ) == String.fromCharCode( 64 + n ) || a.charAt( 8 ) == parseInt( temp.substring( temp.length-1, temp.length ) ) ){
                return 2;
            }else{
                return -2;
            }
        }
        //comprobacion de NIEs
        //T
        if( /^[T]{1}/.test( temp ) ){
            if( a.charAt( 8 ) == /^[T]{1}[A-Z0-9]{8}$/.test( temp ) ){
                return 3;
            }else{
                return -3;
            }
        }
        //XYZ
        if( /^[XYZ]{1}/.test( temp ) ){
            temp = temp.replace( 'X','0' )
            temp = temp.replace( 'Y','1' )
            temp = temp.replace( 'Z','2' )
            pos = temp.substring(0, 8) % 23;
            if( a.toUpperCase().charAt( 8 ) == cadenadni.substring( pos, pos + 1 ) ){
                return 3;
            }else{
                return -3;
            }
        }
    }
    return 0;
}