ip_popup.js

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 saveSettings()
{
    var scriptAddr = document.getElementById("script").value;
    scriptAddr = scriptAddr.trim();

    if (scriptAddr != "")
    {
        if (window.confirm('Save script address ' + scriptAddr + '? Are you sure?'))
        {
            browser.storage.local.set({
                server_settings: {script_addr: scriptAddr}
            });
            window.alert('Settings saved!');
        }
        else
        {
            document.getElementById("script").value = curAddr;
        }
    }
}

function onGot(item)
{
    if (isEmptyObject(item))
    {
        curAddr = defAddr;
    }
    else
    {
        if (item.server_settings.script_addr == '')
        {
            curAddr = defAddr;
        }
        else
        {
            curAddr = item.server_settings.script_addr;
        }
    }
    document.getElementById("script").value = curAddr;
}

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
{
    document.getElementById("flag").src = 'flags/1working.png';
    document.getElementById("flag").alt = 'Working';
    document.getElementById("flag").title = 'working...';

    $.get(curAddr)
        .done (function (data) {
            //data processing code here
            var json = $.parseJSON(data);
            document.getElementById("ip").value = json.ip;
            document.getElementById("country").value = json.country;

            if (json.cc.trim() == '') //no country code
            {
                document.getElementById("flag").src = 'flags/3unknow.png';
                document.getElementById("flag").alt = 'Unknow';
                document.getElementById("flag").title = 'Unknow country code';
            }
            else //country code exist
            {
                document.getElementById("flag").src = 'flags/'+json.cc.trim()+'.png';
                document.getElementById("flag").alt = json.cc;
                document.getElementById("flag").title = json.cc;
            }
        })
        .fail(function () {
            //error processing code here
            document.getElementById("flag").src = 'flags/2error.png';
            document.getElementById("flag").alt = 'Error';
            document.getElementById("flag").title = 'Error';
        });
}

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

function restoreDefaults()
{
    if (window.confirm('Restore defaults?'))
    {
        curAddr = defAddr;
        document.getElementById("script").value = defAddr;
        browser.storage.local.set({
                server_settings: {script_addr: defAddr}
            });
    }
}

document.getElementById("save").addEventListener("click", saveSettings); //скобки не забудь про сраные скобки
document.getElementById("restore").addEventListener("click", restoreDefaults);
document.addEventListener('DOMContentLoaded', bodyLoad);