How to get active window link in chrome extension?

Question

Google Chrome

I can not find out the url of the active window of the browser.
tried like this:
chrome.tabs.onUpdated.addListener(function (tabId, changeInfo, tab) {
alert(tab.url);
});
the console outputs the following:
Uncaught TypeError: Cannot read property 'onUpdated' of undefined
what to do??

Answer 1

Did you write this in the manifest?

"permissions": [
          "tabs"
        ],