create messy reactivity-ish test stuff.

(it works but it's messy.)

src/core.mjs

@@ -12,7 +12,7 @@ export function json_as_html (json, state = new Map()) {
 	}
 
 	if (typeof json === "function") {
-		return json_as_html(json(state), state);
+		return from_function(json, state);
 	}
 
 	const [type, attributes = [], children = []] = json;
@@ -32,3 +32,21 @@ export function json_as_html (json, state = new Map()) {
 	
 	return elem;
 }
+
+// these two functions are pretty messy.
+function from_function (fn, state) {
+	const [after, has_run_after] = delayed(fn => elem => fn(elem));
+	const initial = json_as_html(fn(state, after), state);
+	if (has_run_after()) after(initial);
+	return initial;
+}
+function delayed (fn) {
+	let has_run_once = false;
+	let initial_result = undefined;
+	return [(...args) => {
+		if (has_run_once) return initial_result(...args);
+		has_run_once = true;
+		initial_result = fn(...args);
+		return initial_result;
+	}, _ => has_run_once];
+}

src/demo.mjs

@@ -15,10 +15,16 @@ const demo = [
 		state => ["button", [
 			["onclick", _ => {
 				state.set("clicked", true);
-				render();
+				trigger_event("button_pressed");
 			}]
 		], "it can even do buttons!"],
-		state => ["p", [], state.get("clicked") ? "clicked" : "not clicked"],
+		(state, after) => {
+			// this is very messy.
+			const generate = _ => ["p", [], state.get("clicked") ? "clicked" : "not clicked"];
+			after(elem => listen_event("button_pressed", _ => elem.replaceWith(json_as_html(generate(), state))));
+
+			return generate();
+		},
 		["ul",
 			[],
 			[
@@ -29,11 +35,22 @@ const demo = [
 	],
 ];
 
-const state = new Map();
+let event_listeners = new Map();
+
+function trigger_event (name) {
+	if (event_listeners.has(name)) {
+		event_listeners.get(name).forEach(fn => fn());
+	}
+}
+
+function listen_event (name, fn) {
+	if (!event_listeners.has(name)) event_listeners.set(name, []);
+	event_listeners.get(name).push(fn);
+}
 
 function render () {
 	document.body.innerHTML = "";
-	document.body.appendChild(json_as_html(demo, state));
+	document.body.appendChild(json_as_html(demo));
 }
 
 render();