How to make url parameter in chrome.getCookies changed based on url of active tab

Question

I am currently developing a chrome extension that can get cookies from a website, using chrome.getCookies. However, the url parameter in

chrome.getCookies 

must be a static url in order to work, like this:

chrome.cookies.get({url: 'https://example.org/#/', name: 
'token'}, function(cookie) {
    document.getElementById("token").innerHTML = cookie.value
});

But I want to make that url changed dynamically based on which tab I am using that extension. So I tried this:

var tabUrl;
chrome.tabs.getSelected(null, function(tab) {
    tabUrl = tab.url
});

chrome.cookies.get({url: tabUrl, name: 
'token'}, function(cookie) {
    document.getElementById("token").innerHTML = cookie.value
});

And it didn't work. What should I to to achieve my goal?

Edit: If anyone ever reach this page, here the solution, you have to put subsequent code inside the callback, here's the correct one:

chrome.tabs.getSelected(null, function(tab) {
    chrome.cookies.get({url: tab.url, name: 'expa_token'}, function(cookie) {
    document.getElementById("token").innerHTML = cookie.value
    });
});