Changed
- 💥 [761](https://github.com/plotly/dash/pull/761) Several breaking changes to the `dash.Dash` API:
- Remove two obsolete constructor kwargs: `static_folder` and `components_cache_max_age`
- Remove the misspelled `supress_callback_exceptions` fallback
- Remove the unused `resources.config.infer_from_layout`
- Revamp `app.config`: ALL constructor args are now stored in `config`, with three exceptions: `server`, `index_string`, and `plugins`. None of these are stored in any other instance attributes anymore.
- Change `hot_reload_interval` from msec to seconds, for consistency with `hot_reload_watch_interval`
- When called from `enable_dev_tools`, `debug=True` by default. It's still `False` by default from `run_server`.
- ✨ [744](https://github.com/plotly/dash/pull/744) Introducing Dash Testing (`dash.testing`) - read the full tutorial at <https://dash.plotly.com/testing>.
- [753](https://github.com/plotly/dash/pull/753) `Component` no longer inherits `MutableMapping`, so `values`, `keys`, and more are no longer methods. Fixes an issue reported in [dcc#440](https://github.com/plotly/dash-core-components/issues/440) where components with certain prop names defined but not provided would cause a failure to render. During component generation we now disallow all props with leading underscores or matching a few remaining reserved words: `UNDEFINED`, `REQUIRED`, `to_plotly_json`, `available_properties`, and `available_wildcard_properties`.
- [739](https://github.com/plotly/dash/pull/739) Allow the Flask app to be provided to Dash after object initialization. This allows users to define Dash layouts etc when using the app factory pattern, or any other pattern that inhibits access to the app object. This broadly complies with the flask extension API, allowing Dash to be considered as a Flask extension where it needs to be.
- [774](https://github.com/plotly/dash/pull/774) Allow the Flask app to set the Dash app name if the name is not provided by users.
- [722](https://github.com/plotly/dash/pull/722) Assets are served locally by default. Both JS scripts and CSS files are affected. This improves robustness and flexibility in numerous situations, but in certain cases initial loading could be slowed. To restore the previous CDN serving, set `app.scripts.config.serve_locally = False` (and similarly with `app.css`, but this is generally less important).
- [724](https://github.com/plotly/dash/pull/724), [renderer#175](https://github.com/plotly/dash-renderer/pull/175) Undo/redo toolbar is removed by default, you can enable it with `app=Dash(show_undo_redo=true)`. The CSS hack `._dash-undo-redo:{display:none;}` is no longer needed
- 💥 [709](https://github.com/plotly/dash/pull/709) Merge the `dash-renderer` project into the main dash repo to simplify feature dev workflow. We will keep the [deprecated one](https://github.com/plotly/dash-renderer) for archive purpose.