如何在Javascript中阅读Web服务响应的元素

I'm new in Javascript, PHP and XML. My question goes like this. I'm using this web service http://www.webservicex.net/country.asmx?op=GetCountries (This is the WSDL: http://www.webservicex.net/country.asmx?WSDL) I'm using Jquery BTW. And as part of my app, I'm trying to get every country from the response into an HTML select via Javascript. But I can't find how to get access to every specific element of that response (countries).

These are my pieces of code so far:

PHP

<?php
    $url1 = "http://www.webservicex.net/country.asmx?WSDL";
    $client = new SoapClient($url1);
    $Res = $client->GetCountries();
    echo json_encode($Res);
?>

Javascript

Here I should populate the select when load, but I can't even get access to an element of the response so I'm just trying to print something in a div element for testing purposes.

  window.onload = function() {
                      $.post("process.php", {}, function(response) {
                            var str_res = JSON.parse(response);
                            document.getElementById("Section2").innerHTML = str_res[1];
                            console.log(response);
                       }
      }

I know that "str_res[1]" won't work, but that's exactly what I'm trying to figure out. How do I access the response elements. For example get "Aruba" and print it or add it to the select I mentioned. I hope I was able to explain my concern, and thanks in advance!

Try this

test.html file

<html>
    <body>
        this is html page, wait to load result

        <select id="dropdown"></select>

        <script
                      src="https://code.jquery.com/jquery-3.1.1.min.js"
                      integrity="sha256-hVVnYaiADRTO2PzUGmuLJr8BLUSjGIZsDYGmIJLv2b8="
                      crossorigin="anonymous"></script>
        <script type="text/javascript">
        $.post("test.php", {}, function(response) {
                var str_res = JSON.parse(response); 
               //   console.log(str_res);
                $.each(str_res, function(i, item) {
                    //console.log(str_res[i]);
                    //console.log('-------');   

                    $('#dropdown').append($('<option>', { 
                        value: str_res[i],
                        text : str_res[i] 
                    }));
                });


            });
        </script>


    </body>
</html>

test.php file

<?php
    $url1 = "http://www.webservicex.net/country.asmx?WSDL";
    $client = new SoapClient($url1);
    $Res = $client->GetCountries();

    $xml = simplexml_load_string($Res->GetCountriesResult);
    $data = array();
    foreach ($xml->Table as $key => $value) {
        array_push($data,(string)$value->Name);
    }

    //print_r($data);
    echo json_encode($data);
?>