in chrome extensions how to trigger an event on deactivation?

Question

I have a chrome extension which injects some DOM event listeners through the content scripts. I want to remove those event listeners from the DOM in the event that the user deactivates the plugins, is there a method to do so?

Answer 1

It's an interesting question. It has to do with a concept of "orphaned" scripts. I talk at length about those in an addendum here.

Problem is, as soon as the script becomes detached from the parent extension, Chrome APIs will fail. As such, detecting this is not straightforward.

There are many possible approaches:

1. Maintain an open port to the background page. The port will fire an onDisconnected event in case the background page ceases to exist.

   This is an event-based approach - you will be able to react immediately.

   But this has an important downside: maintaining an open port will prevent an Event page from unloading. So if you use a non-persistent background page, this is not optimal.

2. Periodically, or better yet - in the beginning of your handlers, try to do something with Chrome API. This will fail, and you can catch the exception and assume that the extension is orphaned.

   Please note that this is pretty much undefined behavior. How Chrome API reacts can change over time.

   function heartbeat(success, failure) {
     try {
       if(chrome.runtime.getManifest()) {
         success();
       } else { // will return undefined in an orphaned script
         failure();
       }
     } catch(e) { // currently doesn't happen, but may happen
       failure();
     }
   }
   
   function handler() {
     heartbeat(
       function(){ // hearbeat success
         /* Do stuff */
       }, 
       function(){ // hearbeat failure
         someEvent.removeListener(handler);
         console.log("Goodbye, cruel world!");
       }
     );
   }
   someEvent.addListener(handler);
   

3. Finally, there is a proposal to make a special event for this situation, but it's not implemented yet.

4. Specifically for updates when the extension is reloaded, you can make it inject scripts into existing pages and let old scripts know they should deactivate; however, since your question is about extension being removed, it doesn't help.

With the hard part done, actual removal of event listeners depends on how you added them, but should be straightforward.

Answer 2

1. onDisabled fired when app or extension has been disabled.

   chrome.management.onDisabled.addListener(function callback)
   

2. EventTarget.removeEventListener() removes the event listener previously registered.

   var div = document.getElementById('div');
   var listener = function (event) {
     /* do something here */
   };
   div.addEventListener('click', listener, false);
   div.removeEventListener('click', listener, false);
   

3. I think you don't need to this, since once your extension is disabled, your event listener will be removed and won't be injected.