javascript convert object to string

I have some form with several values depending which is selected

    
        Case1
        ....
        Case20
    
    

Now script

$(document).ready(function() {

    $("#go").click(function() {

        // Obtener la referencia a las listas
        var lista1 = eval(document.getElementById("tropa1"));
        // Obtener el valor de la opción seleccionada
        var valort1 = eval(lista1.options[lista1.selectedIndex].value);
        var cadena = String(valort1);
        console.log("PHP: " + String(valort1));
        if (cadena.indexOf('z') != -1) {
            // value selected in options does not contain 'z'
            console.log("DOES NOT CONTAIN Z");
            console.log(cadena);

            confront(nu1, valort1, nu2, valort2)

        } else {
            //// value selected in options contains 'z'
            console.log("CONTAINS Z");
            console.log(cadena);
        }
    })

});

I tried to make this, but console return : [object Object] and not show string.
even using String() function or eval() to convert object to a string