diff --git a/src/runtime/internal/ResizeObserverSingleton.ts b/src/runtime/internal/ResizeObserverSingleton.ts
index 2fe4ebf4d8..485eed786c 100644
--- a/src/runtime/internal/ResizeObserverSingleton.ts
+++ b/src/runtime/internal/ResizeObserverSingleton.ts
@@ -1,73 +1,66 @@
 import { globals } from './globals';
-
 /**
  * Resize observer singleton.
  * One listener per element only!
  * https://groups.google.com/a/chromium.org/g/blink-dev/c/z6ienONUb5A/m/F5-VcUZtBAAJ
  */
 export class ResizeObserverSingleton {
-	constructor(readonly options?: ResizeObserverOptions) {}
-
-	observe(element: Element, listener: Listener) {
-		this._listeners.set(element, listener);
-		this._getObserver().observe(element, this.options);
-		return () => {
-			this._listeners.delete(element);
-			this._observer.unobserve(element); // this line can probably be removed
-		};
-	}
-
-	private readonly _listeners: WeakMap<Element, Listener> =
-		'WeakMap' in globals ? new WeakMap() : undefined;
-	private _observer?: ResizeObserver;
-	private _getObserver() {
-		return (
-			this._observer ??
-			(this._observer = new ResizeObserver((entries) => {
-				for (const entry of entries) {
-					(ResizeObserverSingleton as any).entries.set(entry.target, entry);
-					this._listeners.get(entry.target)?.(entry);
-				}
-			}))
-		);
-	}
+    options;
+    constructor(options) {
+        this.options = options;
+    }
+    /** @param {Element} element
+     * @param {Listener} listener
+     * @returns {() => void}
+     */
+    observe(element, listener) {
+        this._listeners.set(element, listener);
+        this._getObserver().observe(element, this.options);
+        return () => {
+            this._listeners.delete(element);
+            this._observer.unobserve(element); // this line can probably be removed
+        };
+    }
+    /** @private
+     * @readonly
+     * @default 'WeakMap' in globals ? new WeakMap() : undefined
+     */
+    _listeners = 'WeakMap' in globals ? new WeakMap() : undefined;
+    /** @private */
+    _observer = undefined;
+    /** @private
+     * @returns {ResizeObserver}
+     */
+    _getObserver() {
+        return (this._observer ??
+            (this._observer = new ResizeObserver((entries) => {
+                for (const entry of entries) {
+                    ResizeObserverSingleton.entries.set(entry.target, entry);
+                    this._listeners.get(entry.target)?.(entry);
+                }
+            })));
+    }
 }
 // Needs to be written like this to pass the tree-shake-test
-(ResizeObserverSingleton as any).entries = 'WeakMap' in globals ? new WeakMap() : undefined;
-
-type Listener = (entry: ResizeObserverEntry) => any;
-
-// TODO: Remove this
-interface ResizeObserverSize {
-	readonly blockSize: number;
-	readonly inlineSize: number;
-}
-
-interface ResizeObserverEntry {
-	readonly borderBoxSize: readonly ResizeObserverSize[];
-	readonly contentBoxSize: readonly ResizeObserverSize[];
-	readonly contentRect: DOMRectReadOnly;
-	readonly devicePixelContentBoxSize: readonly ResizeObserverSize[];
-	readonly target: Element;
-}
+ResizeObserverSingleton.entries = 'WeakMap' in globals ? new WeakMap() : undefined;
 
-type ResizeObserverBoxOptions = 'border-box' | 'content-box' | 'device-pixel-content-box';
 
-interface ResizeObserverOptions {
-	box?: ResizeObserverBoxOptions;
-}
-
-interface ResizeObserver {
-	disconnect(): void;
-	observe(target: Element, options?: ResizeObserverOptions): void;
-	unobserve(target: Element): void;
-}
-
-interface ResizeObserverCallback {
-	(entries: ResizeObserverEntry[], observer: ResizeObserver): void;
-}
+/** @typedef {(entry: ResizeObserverEntry) => any} Listener */
+/** @typedef {'border-box' | 'content-box' | 'device-pixel-content-box'} ResizeObserverBoxOptions */
 
-declare let ResizeObserver: {
-	prototype: ResizeObserver;
-	new (callback: ResizeObserverCallback): ResizeObserver;
-};
+/** @typedef {Object} ResizeObserverSize
+ * @property {number} blockSize
+ * @property {number} inlineSize 
+ */
+/** @typedef {Object} ResizeObserverEntry
+ * @property {readonlyResizeObserverSize[]} borderBoxSize
+ * @property {readonlyResizeObserverSize[]} contentBoxSize
+ * @property {DOMRectReadOnly} contentRect
+ * @property {readonlyResizeObserverSize[]} devicePixelContentBoxSize
+ * @property {Element} target 
+ */
+/** @typedef {Object} ResizeObserverOptions
+ * @property {ResizeObserverBoxOptions} [box] 
+ */
+/** @typedef {Object} ResizeObserver */
+/** @typedef {Object} ResizeObserverCallback */
\ No newline at end of file