pageMod attaching workers multiple times

Question

I have encountered this issue while working on an extension. I am attaching a pageMod to the page based on tab ready event to modify the contents of the page, but when I reload the page, the worker seems to get attached one more time, so after 1 reload it loads 2 workers for the same url (no iframes), after 2 reloads it loads 3 workers, etc. Here's the initial code that I started with (I ripped it out of the larger block):

mod = null;   

tabs.on('ready', function(tab) {    
    mod = this.pageMod.PageMod({
        include: ["*"],
        contentScriptFile: ["resource://data/full_page.js"],
        attachTo: ["top", "frame", "existing"],
        onAttach: function(worker) {
            Logger.log('---------> worker.url is ' + worker.url);
        }
    });
}

I was able to remedy this somewhat by destroying the mod on every ready event by attaching this code at the very beginning of the ready event handler.

mod = null;   

tabs.on('ready', function(tab) {
    if (mod) {
        mod.destroy();
    }

    mod = this.pageMod.PageMod({
        include: ["*"],
        contentScriptFile: ["resource://data/full_page.js"],
        attachTo: ["top", "frame", "existing"],
        onAttach: function(worker) {
            Logger.log('---------> worker.url is ' + worker.url);
        }
    });
}

However, I still see that two workers get attached after the first reload, three after the second, etc. I made sure my listener got initialized only once. Anybody encountered this before? Am I not using it correctly? Thanks! Luka

Answer 1

No, you're not using it correctly. A pagemod only needs to be set up once. It automatically attaches on ready. The page mod you created is going attach to every new page (["*"]). And every time a new page loads, a new pagemod is created that attaches to every new tab...

If you want to insert a content script into every page, just get rid of the on ready listener.

    mod = this.pageMod.PageMod({
        include: ["*"],
        contentScriptFile: ["./full_page.js"],
        attachTo: ["top", "frame", "existing"],
        onAttach: function(worker) {
            Logger.log('---------> worker.url is ' + worker.url);
        }
    });

If you want to use the on ready listener for a specific tab, attach a script to the tab:

tabs.on('ready', function(tab) {    
    var worker = tab.attach({
        contentScriptFile: ["./full_page.js"]
    });
    Logger.log('---------> worker.url is ' + worker.url);
}