destroy and node Middleware

[agubler]

Type: feature

The following has been addressed in the PR:

• There is a related issue
• All code has been formatted with prettier as per the readme code style guidelines
• Unit or Functional tests are included in the PR

Description:

Adds two new core middleware implementations, destroy and getDom

destroy

Registers a destroy handle that is called when a widget is removed.

const factory = create({ destroy });

const MyWidget = factory(({ middleware: { destroy } }) => {
	destroy(() => {
		// do something when the widget is removed
	});
	return v('div', { key: 'div' });
});

Limited to registering a single handle per unique middleware, for use-cases that require conditional or multiple handles through out the lifetime of a widget the user is required to manage this within their own middleware.

const factory = create({ destroy });

const myMiddleware = factory(({ middleware: { destroy } }) => {
	const destroyFunctions: (() => void)[] = [];
	destroy(() => {
		let handle: () => void | undefined;
		while (cb = destroyFunctions.pop()) {
			cb();
		}
	});
	return {
		foo() {
			// add destroy to `destroyFunctions` array
		}
	}
});

If destroy is called more than once for a widget or middleware it will be ignored.

node

Returns the DOM node for the key of a VNode in a widget.

const factory = create({ node });

const myMiddleware = factory(({ middleware: { node } }) => {
	return {
		doSomething(key: string | number) {
			const node = node.get(key);
			// do something with the node, like return dimensions.
	};
});

Related to #352

[agubler]

@matt-gadd updated from getDom to node for the middleware that returns the DOM node for a particular key.