window.open returns undefined in chrome extension

Question

I have content script based Chrome extension. I initiate the sign in process through a popup window in the content script.

I open a popup window using the below code and then wait till its closed.

However, I get an 'undefined' from window.open method. Does anybody know why this happens?

loginwin is undefined in below code although the popup window opens up fine with the specified login_url. The code below is called from my content script.

var loginWin = window.open(login_url, 'LoginWindow', "width=655,height=490");
console.log(loginWin);
// Check every 100 ms if the popup is closed.
var finishedInterval = setInterval(function() {
    console.log('checking if loginWin closed');
    if (loginWin.closed) {
        clearInterval(finishedInterval);
        console.log('popup is now closed');
        Backbone.history.navigate('index', true);
    }
}, 1000);

Answer 1

Note: This answer is obsolete. window.open() in a Chrome extension always returns either null (when the popup is blocked) or a window object. The information below only applies to very old (2012) versions of Chrome.

---

Content scripts do not have any access to a page's global window object. For content scripts, the following applies:

• The window variable does not refer to the page's global object. Instead, it refers to a new context, a "layer" over the page. The page's DOM is fully accessible. ^{#execution-environment}

Given a document consisting of   <iframe id="frameName" src="http://domain/"></iframe>:

• Access to the contents of a frame is restricted by the Same origin policy of the page; the permissions of your extension does not relax the policy.
• frames[0] and frames['frameName'], (normally referring to the the frame's containing global window object) is undefined.
• var iframe = document.getElementById('frameName');
  • iframe.contentDocument returns a document object of the containing frame, because content scripts have access to the DOM of a page. This property is null when the Same origin policy applies.
  • iframe.contentDocument.defaultView (refers to the window object associated with the document) is undefined.
  • iframe.contentWindow is undefined.

As you can see, window.open() does not return a Window instance (neither does window.opener, and so forth).

---

Alternatives

• Inject the code in the page, so that it runs in the context of the page. Note: Only use this method if the page you're operating on can be trusted. To communicate between the injected script and the content script, you could use:

  var login_url = 'http://example.com/';
  var event_name = 'robwuniq' + Math.random().toString(16); // Unique name
  document.addEventListener(event_name, function localName() {
      document.removeEventListener(event_name, localName); // Clean-up
      // Your logic:
      Backbone.history.navigate('index', true);
  });
  // Method 2b: Inject code which runs in the context of the page
  var actualCode = '(' + function(login_url, event_name) {
      var loginWin = window.open(login_url, 'LoginWindow', "width=655,height=490");
      console.log(loginWin);
      // Check every 100 ms if the popup is closed.
      var finishedInterval = setInterval(function() {
          console.log('checking if loginWin closed');
          if (loginWin.closed) {
              clearInterval(finishedInterval);
              console.log('popup is now closed');
              // Notify content script
              var event = document.createEvent('Events');
              event.initEvent(event_name, false, false);
              document.dispatchEvent(event);
          }
      }, 1000);
  } + ')(' + JSON.stringify(login_url+'') + ', "' + event_name + '")';
  var script = document.createElement('script');
  script.textContent = actualCode;
  (document.head||document.documentElement).appendChild(script);
  script.parentNode.removeChild(script);
  

• Launch the window from the background page using window.open(). This returns a window object which has a reliable closed property. See the next bullet point for more details on the communication flow.

• From the content script, pass a message to the background page. In the background page, use chrome.windows.create to open a window. In the callback, assign an chrome.tabs.onRemoved and/or chrome.tabs.onUpdated event. When these event listeners are triggered, they should remove themselves, and notify the original caller (content script) using the sendResponse function of chrome.extension.onMessage.

Answer 2

In my case, Chrome was blocking the popup and the user had to unblock by clicking the "blocked popup" icon in the upper-right corner of the window. (They can also enable/disable exceptions under "Content settings..." in Chrome settings.)

I would suggest adding some code after window.open() so that the user knows what to do. For example:

if (!loginWin)
    alert("You must first unblock popups and try again for this to work!");