:date: 2021-02-23

==========================
Tuesday, February 23, 2021
==========================


I read the docs about PrimeReact's DataTable:

https://www.primefaces.org/primereact/showcase/#/datatable

The example uses axios. What's that? Here a nice introduction:

https://dev.to/veewebcode/what-is-axios-and-how-to-use-it-4an1

Might be useful to play around with it. But not now.

I still don't fully understand what's a state in React.

A `<DataTable>` component needs at least a `value` attribute.
And its children must be a `<Column>` components, one child per column).

Once more, npm asks me to upgrade, and I do it::

  npm notice New patch version of npm available! 7.5.4 -> 7.5.6
  npm notice Changelog: https://github.com/npm/cli/releases/tag/v7.5.6
  npm notice Run npm install -g npm@7.5.6 to update!

  $ sudo npm install -g npm

I get this warning in my JS console:

  Warning: Can't perform a React state update on an unmounted component. This is
  a no-op, but it indicates a memory leak in your application. To fix, cancel
  all subscriptions and asynchronous tasks in the componentWillUnmount method.

This warning is caused by the `<DataProvider>`, a component used by the
`<DashboardItems>` component.
The `<DashboardItems>` component has a dynamic list of children.

I guess that the warning means "When you start a polyfill request in
componentDidMount(), then you should make sure to cancel it before the component
gets unmounted."

So how to cancel a polyfill request? The `whatwg-fetch docs
<https://www.npmjs.com/package/whatwg-fetch>`_ has a section "Aborting
requests". Wow:  "aborting a fetch requires use of two additional DOM APIs:
AbortController and AbortSignal. ... Consequently, you will need to include an
additional polyfill for these APIs to abort fetches". But the example seems to
do what I want, so I integrated it in `DataProvider.js`  (unlike the example I
must create the abort controller during the component's construct method, i.e.
we have one such controller for every data provider...)

Funny: I got the warning "DataProvider has a method called
componentDidUnmount(). But there is no such lifecycle method. Did you mean
componentWillUnmount()?", and the warning was right...

So this added a new dependency::

  $ npm install yet-another-abortcontroller-polyfill --save

Yes, one warning less! So I understood the reason for a problem and managed to
fix it. I guess that it wasn't a huge problem, and my actual problem
(:ticket:`3981`) is still there, but an encouraging experience nevertheless.

I discovered that the problem starts somewhere in :meth:`LinoGrid.onEditorInit`.