Old ExtJS API documentation, hosted here for convenience because Sencha doesn't host them anymore.
http://galgeri.github.io/extjs-docs-archive/
Clone the project:
git clone https://github.com/galgeri/extjs-docs-archive.git
Since the Ext docs webapp uses ajax, you also need to run a simple web server to use it. For example,
python -m http.server
Then you should be able to go to http://localhost:8000 and view it.