WIP implement NavigateEvent.sourceElement

[tchak]

https://developer.mozilla.org/en-US/docs/Web/API/NavigateEvent/sourceElement

This is very much a WIP. I am still trying to figure out how and where to add tests. However, I wanted to open a conversation about it and get your early feedback in case I am going down the wrong path regarding how to implement this.

[fabiancook]

Hi, tests are added into the src/tests folder, the tests are ran across multiple environments so a single testing framework hasn't yet been included.

The idea with the test files is that if they exit successfully, its good, exit with an error, its a failing test.

For this PR, a test would be added to the navigation.scope tests, these run when we're in a browser with some form of navigation, which could also be the real implementation of navigation from the browser.

There is an anchor event test here, which should be extendable to check that sourceElement was added too

navigation/src/tests/navigation.scope.ts

Lines 147 to 175 in 6f66ed2

	const anchor = document.createElement("a");
	const randomUrl = `/random/${Math.random()}`;
	anchor.href = randomUrl;
	anchor.download = `named-${Math.random()}.png`;
	anchor.id = "test-click-me";
	const anchorPromise = new Promise<NavigateEvent>(
	resolve => {
	collection.addEventListener(
	"navigate",
	event => {
	if (new URL(event.destination.url).pathname === randomUrl) {
	resolve(event);
	}
	}
	)
	}
	);
	document.body.appendChild(anchor);
	anchor.click();
	const anchorEvent = await anchorPromise;
	ok<NavigateEvent>(anchorEvent);
	console.log("Anchor event seen:", anchorEvent.type, anchorEvent.originalEvent?.type, anchorEvent.destination.url);

e.g.

ok(anchorEvent.sourceElement, "Expected source element")