magic objects

packages/svelte/src/internal/client/magic.js

@@ -0,0 +1,75 @@
+import { effect_active, get, set, increment, source } from './runtime.js';
+
+/**
+ * @template T
+ * @param {T} value
+ * @returns {T}
+ */
+export function magic(value) {
+	if (value && typeof value === 'object') {
+		if (Array.isArray(value)) {
+			// TODO
+		}
+
+		return object(value);
+	}
+
+	return value;
+}
+
+/**
+ * @template {Record<string | symbol, any>} T
+ * @param {T} value
+ * @returns {T}
+ */
+function object(value) {
+	/** @type {Map<string | symbol, any>} */
+	const sources = new Map();
+	let version = source(0);
+
+	return new Proxy(value, {
+		get(target, prop, receiver) {
+			let s = sources.get(prop);
+
+			if (effect_active() && !s) {
+				s = source(magic(target[prop]));
+				sources.set(prop, s);
+			}
+
+			let value = s ? get(s) : target[prop];
+
+			if (typeof value === 'function') {
+				return (...args) => {
+					return value.apply(receiver, args);
+				};
+			}
+
+			return value;
+		},
+		set(target, prop, value) {
+			const s = sources.get(prop);
+			if (s) set(s, magic(value));
+
+			if (!(prop in target)) increment(version);
+			target[prop] = value;
+
+			return true;
+		},
+		deleteProperty(target, prop) {
+			const s = sources.get(prop);
+			if (s) set(s, undefined);
+
+			if (prop in target) increment(version);
+
+			return delete target[prop];
+		},
+		has(target, prop) {
+			get(version);
+			return Reflect.has(target, prop);
+		},
+		ownKeys(target) {
+			get(version);
+			return Reflect.ownKeys(target);
+		}
+	});
+}

packages/svelte/src/internal/index.js

@@ -56,3 +56,5 @@ export {
 } from './client/operations.js';
 
 export { raf } from './client/timing.js';
+
+export { magic } from './client/magic.js';

packages/svelte/src/main/main-client.js

@@ -255,4 +255,12 @@ export function afterUpdate(fn) {
 
 // TODO bring implementations in here
 // (except probably untrack — do we want to expose that, if there's also a rune?)
-export { flushSync, createRoot, mount, tick, untrack, onDestroy } from '../internal/index.js';
+export {
+	flushSync,
+	createRoot,
+	mount,
+	tick,
+	untrack,
+	onDestroy,
+	magic
+} from '../internal/index.js';