Firefox Add-On SDK: Run content script in new tab only once

Question

I am trying to develop a simple add-on for Firefox which should work something like this:

1. User clicks item in context menu.
2. New tab is opened.
3. Content (innerHTML) of the new tab is overridden using content script.

Also, the content script should only be executed once, so that if the user would enter a website in the new tab the script should not be executed.

I've got it working with editing the new tabs content, but my only problem is to have the content script run only once when the tab is opened. In the code I have at the moment the script run every time a page has been loaded in the tab:

var contextMenu = require("sdk/context-menu");
var tabs = require("sdk/tabs");

var menuItem = contextMenu.Item({
    label: "Test",
    contentScript: 'self.on("click", function () { self.postMessage(); })',
    onMessage: function (data) {
        newTab();
    }
});

function newTab () {
    tabs.open("about:blank");

    tabs.activeTab.on('ready', function (tab) {
        tab.attach({
            contentScript: 'document.body.innerHTML = "testing";'
        });
    });
}

I'm guessing there's a way to have this run only the first time the tab is "ready". Seems like a simple task but I can't figure out how to do this. Anyone got any tips?

Answer 1

Use tabs.activeTab.once(); instead of tabs.activeTab.on();. This way the listener gets detached once it intercepts the first message.