wbamberg Improve content script injection (#240)
* Improve content script injection

* Add an error handler for content script injection

* Use a guard variable in the content script, instead

* Fix comment

* Ensure tabID is unchanged; fix image styles

* Only inject script once; use CSS to hide page

* Display an error when the script can't be executed; document other limitations

* Log error on script execute failure
Latest commit 37cb9f7 Nov 1, 2017



What it does

The extension includes:

  • a browser action with a popup including HTML, CSS, and JS
  • a content script
  • three images, each of a different beast, packaged as web accessible resources

When the user clicks the browser action button, the popup is shown, enabling the user to choose one of three beasts.

When it is shown, the popup injects a content script into the current page.

When the user chooses a beast, the extension sends the content script a message containing the name of the chosen beast.

When the content script receives this message, it replaces the current page content with an image of the chosen beast.

When the user clicks the reset button, the page reloads, and reverts to its original form.

Note that:

  • if the user reloads the tab, or switches tabs, while the popup is open, then the popup won't be able to beastify the page any more (because the content script was injected into the original tab).

  • by default tabs.executeScript() injects the script only when the web page and its resources have finished loading. This means that clicks in the popup will have no effect until the page has finished loading.

  • it's not possible to inject content scripts into certain pages, including privileged browser pages like "about:debugging" and the addons.mozilla.org website. If the user clicks the beastify icon when such a page is loaded into the active tab, the popup displays an error message.

What it shows

  • write a browser action with a popup
  • how to have different browser_action images based upon the theme
  • give the popup style and behavior using CSS and JS
  • inject a content script programmatically using tabs.executeScript()
  • send a message from the main extension to a content script
  • use web accessible resources to enable web pages to load packaged content
  • reload web pages