Set a variable from variable array outta options.html into background.js in Chrome extension

Question

I create a Chrome extension and want add an option page where a radio buttons sets a variable from variable array in background.js.

I have background.js with a code like

var xhr = new XMLHttpRequest();
var protocol = "https://";
var country = ["de","ch"];
var middle = ".sistrix.com/toolbox/__loadModule/domain/";
var d = currentDomain();
var end = ".html";

xhr.open("GET", protocol+country+middle+d+end, true);

Further i have a file options.html, containing this code

<select>
  <option value="de">Germany</option>
  <option value="ch">Swiss</option>
</select>

Now i want that selecting of an option in options.html () sets corresponding variable from an array var country = ["de","ch"]; into xhr.open("GET", protocol+country+middle+d+end, true); as country.

Scenario:

• user clicks with the right mouse button on the extension icon
• options page is opened,
• user selects an option, i.e. de - Germany
• after this and until user sets another option, background.js uses corresponding variable de from variable array var country = ["de","ch"]; in xhr.open as country.

PS: some answers about passing data from popup to background don't match my need. I want to have options explicitely under options - here https://easycaptures.com/fs/uploaded/1232/thumbs/7819701093_b.jpg, not in popup, which opens after clicking with the left mouse button on extension icon.