id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,pull_request,body,repo,type,active_lock_reason,performed_via_github_app,reactions,draft,state_reason
1651082214,PR_kwDOBm6k_c5NcFCf,2052,"feat: Javascript Plugin API (Custom panels, column menu items with JS actions)",9020979,open,0,15178711,,16,2023-04-02T20:23:44Z,2023-07-12T16:38:28Z,,FIRST_TIME_CONTRIBUTOR,simonw/datasette/pulls/2052,"## Motivation

- Allow plugins that add data visualizations [`datasette-vega`](https://github.com/simonw/datasette-vega), [`datasette-leaflet`](https://github.com/simonw/datasette-leaflet), and [`datasette-nteract-data-explorer`](https://github.com/hydrosquall/datasette-nteract-data-explorer) to co-exist safely
- Standardize APIs / hooks to ease development for new JS plugin developers (better compat with datasette-lite) through standardized DOM selectors, methods for extending the existing Table UI. This has come up as a feature request several times (see research notes for examples)
- Discussion w/ @simonw about a general-purpose Datasette JS API

## Changes

Summary: Provide 2 new surface areas for Datasette JS plugin developers

1. Custom column header items: <https://a.cl.ly/Kou97wJr>
2. Basic ""panels"" controlled by buttons: <https://a.cl.ly/rRugWobd>

### User Facing Changes

- Allow creating menu items under table header that triggers JS (instead of opening hrefs per the existing [menu_link](https://docs.datasette.io/en/stable/plugin_hooks.html#menu-links-datasette-actor-request) hook). Items can respond to any column metadata provided by the column header (e.g. label). The proof of concept plugins log data to the console, or copy the column name to clipboard.
- Allow plugins to register UI elements in a panel controller. The parent component handles switching the visibility of active plugins.
  - Because native button elements are used, the panel is keyboard-accessible - use tab / shift-tab to cycle through tab options, and `enter` to select.
  - There's room to improve the styling, but the focus of this PR is on the API rather than the UX.

### (plugin) Developer Facing Changes

- Dispatch a `datasette_init` [CustomEvent](https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent/CustomEvent) when the `datasetteManager` is finished loading.
- Provide `manager.registerPlugin` API for adding new functionality that coordinates with Datasette lifecycle events.
- Provide a `manager.selectors` map of DOM elements that users may want to hook into.
  - Updated `table.js` to use refer to these to motivating keeping things in sync
- Allow plugins to register themselves with 2 hooks:
  - `makeColumnActions`: Add items to menu in table column headers. Users can provide a `label`, and either `href` or `onClick` with full access to the metadata for the clicked column (name, type, misc. booleans)
  - `makeAboveTablePanelConfigs`: Add items to the panel. Each panel has a unique ID (namespaced within that plugin), a render function, and a string label.

See [this file](https://github.com/simonw/datasette/blob/2d92b9328022d86505261bcdac419b6ed9cb2236/datasette/static/table-example-plugins.js) for example plugin usage.

###  Core Developer Facing Changes

- Modified `table.js` to make use of the `datasetteManager` API.
- Added example plugins to the `demos/plugins` folder, and stored the test js in the `statics/` folder

## Testing

For Datasette plugin developers, please see the [alpha-level documentation](https://github.com/simonw/datasette/pull/2052#issuecomment-1510423051) .

To run the examples:

```bash
datasette serve fixtures.db  --plugins-dir=demos/plugins/
```

Open local server: `http://127.0.0.1:8001/fixtures/facetable`

Open to all feedback on this PR, from API design to variable naming, to what additional hooks might be useful for the future.

My focus was more on the general shape of the API for developers, rather than on the UX of the test plugins.

## Design notes

- The manager tab panel could be a separate plugin if the implementation is too custom.
- The `makeColumnHeaderItems` benefits from hooking into the logic of `table.js`
- I wanted to offer this to the Datasette core, since the `datasette-manager` would be more powerful if it were connected to lifecycle and JS events that are part of the existing table.js.
- Non-goals:
  - Dependency management (for now) - there's no ""build"" step, we don't know when new plugins will be added. While there are some valid use cases (for example, allow multiple plugins to wait for a global leaflet object to be loaded), I don't see enough use-cases to justify doing this yet.
  - Enabling single-page-app features - for now, most datasette actions lead to a new page being loaded. SPA development offers some benefits (no page jumping after clicking on a link), but also complexity that doesn't need to be in the core Datasette project.

## Research Notes

- Relocated to a [comment](https://github.com/simonw/datasette/pull/2052#issuecomment-1510423215), as this isn't required to review when evaluating the plugin. Including it just for those who are curious.
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