ip_background.js (background script for firefox addon)

var defAddr='https://api.myip.com/';
var curAddr='';

function isEmptyObject(obj)
{
    for (var i in obj)
    {
        if (obj.hasOwnProperty(i))
        {
            return false;
        }
    }
    return true;
}

function onGot(item)
{
    if (isEmptyObject(item))
    {
        curAddr = defAddr;
    }
    else
    {
        if (item.server_settings.script_addr == '')
        {
            curAddr = defAddr;
        }
        else
        {
            curAddr = item.server_settings.script_addr;
        }
    }
}

function onGotError(error)
{
    window.alert(`Error: ${error}`);
}

function loadSettings()
{
    var gettingItem = browser.storage.local.get('server_settings');
    return gettingItem.then(onGot, onGotError);
}

function doRequest() //main request function
{
    var btitle = '';

    browser.browserAction.setIcon({
        path: 'flags/1working.png'
    });
    btitle = "Working...";
    browser.browserAction.setTitle({title: btitle});

    $.get(curAddr)
        .done (function (data) {
            //data processing code here
            var json = $.parseJSON(data);

            if (json.cc.trim() == '') //no country code
            {
                browser.browserAction.setIcon({
                    path: 'flags/3unknow.png'
                });
                btitle = json.ip + " " + "Unknow country";
                browser.browserAction.setTitle({title: btitle});
            }
            else //country code exist
            {
                browser.browserAction.setIcon({
                    path: 'flags/' + json.cc.trim() + '.png'
                });
                btitle = json.ip + " " + json.country + " (" + json.cc + ")";
                browser.browserAction.setTitle({title: btitle});
            }
        })
        .fail(function () {
            //error processing code here
            browser.browserAction.setIcon({
                    path: 'flags/2error.png'
            });
            btitle = "Error";
            browser.browserAction.setTitle({title: btitle});
        });
}

function listinerRun()
{
    loadSettings()
    .then(doRequest);
}

browser.tabs.onActivated.addListener(listinerRun);
browser.tabs.onCreated.addListener(listinerRun);
browser.tabs.onUpdated.addListener(listinerRun);