OperaExtensionShowFilteredContent is a project mainly written in JavaScript, it's free.
A simple Opera extension that shows which URLs have been blocked in the current page
Show Filtered Content is a very simple Opera extension that shows how to use OAuth (and the Opera Link API) from Javascript. It connects to the Opera Link API to get your "Content Blocker" URLs and it shows of many elements are blocked in the current page (eg. if you're wondering if there's anything missing on the page because it's blocked, you can click on the pop-up and find out).
Check these links for more information on the Opera Link API:
For the OAuth part, I'm using this Javascript OAuth library.
Except the file oauth.js (see that file's header for copyright
information), sha1.js (ditto) and icons/button.png, the rest of
the distribution is released under the Apache License:
Copyright 2011 Opera Software ASA
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.