From a1f57aca4d32c4dc18e3e4ec3e2e2b51900fadd0 Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Thu, 14 Mar 2024 11:33:32 +0100
Subject: [PATCH 01/14] Strict type checking

---
 packages/interactivity/tsconfig.json | 11 +++++++++--
 tsconfig.base.json                   |  2 +-
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/packages/interactivity/tsconfig.json b/packages/interactivity/tsconfig.json
index 0fb91956773f89..445fce42e73e54 100644
--- a/packages/interactivity/tsconfig.json
+++ b/packages/interactivity/tsconfig.json
@@ -4,8 +4,15 @@
 	"compilerOptions": {
 		"rootDir": "src",
 		"declarationDir": "build-types",
-		"checkJs": false,
-		"strict": false
+
+		"alwaysStrict": false,
+		"strictNullChecks": false,
+		"strictBindCallApply": false,
+		"strictFunctionTypes": false,
+		"strictPropertyInitialization": false,
+		"noImplicitAny": false,
+		"noImplicitThis": false,
+		"useUnknownInCatchVariables": false
 	},
 	"include": [ "src/**/*" ]
 }
diff --git a/tsconfig.base.json b/tsconfig.base.json
index 1b30522ee52366..18388b7f71854c 100644
--- a/tsconfig.base.json
+++ b/tsconfig.base.json
@@ -7,7 +7,7 @@
 		"jsx": "preserve",
 		"target": "esnext",
 		"module": "esnext",
-		"lib": [ "dom", "esnext" ],
+		"lib": [ "DOM", "DOM.Iterable", "ESNext" ],
 		"declaration": true,
 		"declarationMap": true,
 		"composite": true,

From a7e5048f11cc0d9007c706c45e7895786150fe11 Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 16:09:26 +0200
Subject: [PATCH 02/14] rename to tsx

---
 packages/interactivity/src/{directives.js => directives.tsx} | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename packages/interactivity/src/{directives.js => directives.tsx} (100%)

diff --git a/packages/interactivity/src/directives.js b/packages/interactivity/src/directives.tsx
similarity index 100%
rename from packages/interactivity/src/directives.js
rename to packages/interactivity/src/directives.tsx

From 879b740209e2bfff436cad15ba4bf732265d5df6 Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 17:01:54 +0200
Subject: [PATCH 03/14] isPlainObject

---
 packages/interactivity/src/directives.tsx | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/interactivity/src/directives.tsx b/packages/interactivity/src/directives.tsx
index b19067bdc1ad9a..780910ca66cd2c 100644
--- a/packages/interactivity/src/directives.tsx
+++ b/packages/interactivity/src/directives.tsx
@@ -22,8 +22,8 @@ const contextObjectToProxy = new WeakMap();
 const contextProxyToObject = new WeakMap();
 const contextObjectToFallback = new WeakMap();
 
-const isPlainObject = ( item ) =>
-	item && typeof item === 'object' && item.constructor === Object;
+const isPlainObject = ( item: unknown ): boolean =>
+	Boolean( item && typeof item === 'object' && item.constructor === Object );
 
 const descriptor = Reflect.getOwnPropertyDescriptor;
 

From 361596bc7472e25e4c327bf18ba350476cccfc38 Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 17:05:34 +0200
Subject: [PATCH 04/14] hooks types

---
 packages/interactivity/src/hooks.tsx | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/packages/interactivity/src/hooks.tsx b/packages/interactivity/src/hooks.tsx
index 00c3c0d6d1729d..bc38a67d5b85ad 100644
--- a/packages/interactivity/src/hooks.tsx
+++ b/packages/interactivity/src/hooks.tsx
@@ -1,5 +1,8 @@
 /* @jsx createElement */
 
+// eslint-disable-next-line eslint-comments/disable-enable-pair
+/* eslint-disable react-hooks/exhaustive-deps */
+
 /**
  * External dependencies
  */
@@ -17,7 +20,7 @@ import type { VNode, Context, RefObject } from 'preact';
  */
 import { store, stores, universalUnlock } from './store';
 interface DirectiveEntry {
-	value: string | Object;
+	value: string | object;
 	namespace: string;
 	suffix: string;
 }
@@ -101,7 +104,7 @@ const immutableError = () => {
 		'Please use `data-wp-bind` to modify the attributes of an element.'
 	);
 };
-const immutableHandlers = {
+const immutableHandlers: ProxyHandler< object > = {
 	get( target, key, receiver ) {
 		const value = Reflect.get( target, key, receiver );
 		return !! value && typeof value === 'object'
@@ -111,7 +114,7 @@ const immutableHandlers = {
 	set: immutableError,
 	deleteProperty: immutableError,
 };
-const deepImmutable = < T extends Object = {} >( target: T ): T => {
+const deepImmutable = < T extends object = {} >( target: T ): T => {
 	if ( ! immutableMap.has( target ) )
 		immutableMap.set( target, new Proxy( target, immutableHandlers ) );
 	return immutableMap.get( target );
@@ -258,7 +261,7 @@ export const directive = (
 };
 
 // Resolve the path to some property of the store object.
-const resolve = ( path, namespace ) => {
+const resolve = ( path: string, namespace: string ) => {
 	let resolvedStore = stores.get( namespace );
 	if ( typeof resolvedStore === 'undefined' ) {
 		resolvedStore = store( namespace, undefined, {

From 553d5de170197b281d62eb3baba749398b247489 Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 17:47:58 +0200
Subject: [PATCH 05/14] types

---
 packages/interactivity/src/directives.tsx | 66 +++++++++++++----------
 packages/interactivity/src/hooks.tsx      | 10 ++--
 2 files changed, 46 insertions(+), 30 deletions(-)

diff --git a/packages/interactivity/src/directives.tsx b/packages/interactivity/src/directives.tsx
index 780910ca66cd2c..e2a118e163e17a 100644
--- a/packages/interactivity/src/directives.tsx
+++ b/packages/interactivity/src/directives.tsx
@@ -1,9 +1,12 @@
+// eslint-disable-next-line eslint-comments/disable-enable-pair
+/* eslint-disable react-hooks/exhaustive-deps */
+
 /* @jsx createElement */
 
 /**
  * External dependencies
  */
-import { h as createElement } from 'preact';
+import { h as createElement, type RefObject } from 'preact';
 import { useContext, useMemo, useRef } from 'preact/hooks';
 import { deepSignal, peek } from 'deepsignal';
 
@@ -36,12 +39,12 @@ const descriptor = Reflect.getOwnPropertyDescriptor;
  * By default, all plain objects inside the context are wrapped, unless it is
  * listed in the `ignore` option.
  *
- * @param {Object} current   Current context.
- * @param {Object} inherited Inherited context, used as fallback.
+ * @param current   Current context.
+ * @param inherited Inherited context, used as fallback.
  *
- * @return {Object} The wrapped context object.
+ * @return The wrapped context object.
  */
-const proxifyContext = ( current, inherited = {} ) => {
+const proxifyContext = ( current: object, inherited: object = {} ): object => {
 	// Update the fallback object reference when it changes.
 	contextObjectToFallback.set( current, inherited );
 	if ( ! contextObjectToProxy.has( current ) ) {
@@ -126,10 +129,10 @@ const proxifyContext = ( current, inherited = {} ) => {
 /**
  * Recursively update values within a deepSignal object.
  *
- * @param {Object} target A deepSignal instance.
- * @param {Object} source Object with properties to update in `target`
+ * @param target A deepSignal instance.
+ * @param source Object with properties to update in `target`
  */
-const updateSignals = ( target, source ) => {
+const updateSignals = ( target: object, source: object ) => {
 	for ( const k in source ) {
 		if (
 			isPlainObject( peek( target, k ) ) &&
@@ -145,23 +148,23 @@ const updateSignals = ( target, source ) => {
 /**
  * Recursively clone the passed object.
  *
- * @param {Object} source Source object.
- * @return {Object} Cloned object.
+ * @param source Source object.
+ * @return Cloned object.
  */
-const deepClone = ( source ) => {
+function deepClone< T >( source: T ): T {
 	if ( isPlainObject( source ) ) {
 		return Object.fromEntries(
-			Object.entries( source ).map( ( [ key, value ] ) => [
+			Object.entries( source as object ).map( ( [ key, value ] ) => [
 				key,
 				deepClone( value ),
 			] )
-		);
+		) as T;
 	}
 	if ( Array.isArray( source ) ) {
-		return source.map( ( i ) => deepClone( i ) );
+		return source.map( ( i ) => deepClone( i ) ) as T;
 	}
 	return source;
-};
+}
 
 const newRule =
 	/(?:([\u0080-\uFFFF\w-%@]+) *:? *([^{;]+?);|([^;}{]*?) *{)|(}\s*)/g;
@@ -175,10 +178,10 @@ const empty = ' ';
  * Made by Cristian Bote (@cristianbote) for Goober.
  * https://unpkg.com/browse/goober@2.1.13/src/core/astish.js
  *
- * @param {string} val CSS string.
- * @return {Object} CSS object.
+ * @param val CSS string.
+ * @return CSS object.
  */
-const cssStringToObject = ( val ) => {
+const cssStringToObject = ( val: string ): object => {
 	const tree = [ {} ];
 	let block, left;
 
@@ -202,11 +205,10 @@ const cssStringToObject = ( val ) => {
  * Creates a directive that adds an event listener to the global window or
  * document object.
  *
- * @param {string} type 'window' or 'document'
- * @return {void}
+ * @param type 'window' or 'document'
  */
 const getGlobalEventDirective =
-	( type ) =>
+	( type: 'window' | 'document' ) =>
 	( { directives, evaluate } ) => {
 		directives[ `on-${ type }` ]
 			.filter( ( { suffix } ) => suffix !== 'default' )
@@ -217,7 +219,7 @@ const getGlobalEventDirective =
 					globalVar.addEventListener( entry.suffix, cb );
 					return () =>
 						globalVar.removeEventListener( entry.suffix, cb );
-				}, [] );
+				} );
 			} );
 	};
 
@@ -314,9 +316,13 @@ export default () => {
 						 * need deps because it only needs to do it the first time.
 						 */
 						if ( ! result ) {
-							element.ref.current.classList.remove( className );
+							(
+								element.ref as RefObject< HTMLElement >
+							 ).current!.classList.remove( className );
 						} else {
-							element.ref.current.classList.add( className );
+							(
+								element.ref as RefObject< HTMLElement >
+							 ).current!.classList.add( className );
 						}
 					} );
 				} );
@@ -345,9 +351,13 @@ export default () => {
 					 * because it only needs to do it the first time.
 					 */
 					if ( ! result ) {
-						element.ref.current.style.removeProperty( styleProp );
+						(
+							element.ref as RefObject< HTMLElement >
+						 ).current!.style.removeProperty( styleProp );
 					} else {
-						element.ref.current.style[ styleProp ] = result;
+						(
+							element.ref as RefObject< HTMLElement >
+						 ).current!.style[ styleProp ] = result;
 					}
 				} );
 			} );
@@ -367,7 +377,8 @@ export default () => {
 				 * first time. After that, Preact will handle the changes.
 				 */
 				useInit( () => {
-					const el = element.ref.current;
+					const el = ( element.ref as RefObject< HTMLElement > )
+						.current!;
 
 					/*
 					 * We set the value directly to the corresponding HTMLElement instance
@@ -476,6 +487,7 @@ export default () => {
 			element,
 			evaluate,
 		} ) => {
+			// @ts-expect-error: template type is currently missing https://github.com/preactjs/preact/pull/4334
 			if ( element.type !== 'template' ) return;
 
 			const { Provider } = inheritedContext;
diff --git a/packages/interactivity/src/hooks.tsx b/packages/interactivity/src/hooks.tsx
index bc38a67d5b85ad..be7a053ec90081 100644
--- a/packages/interactivity/src/hooks.tsx
+++ b/packages/interactivity/src/hooks.tsx
@@ -11,6 +11,7 @@ import {
 	options,
 	createContext,
 	cloneElement,
+	type ComponentChildren,
 } from 'preact';
 import { useRef, useCallback, useContext } from 'preact/hooks';
 import type { VNode, Context, RefObject } from 'preact';
@@ -35,11 +36,14 @@ interface DirectiveArgs {
 	/**
 	 * Props present in the current element.
 	 */
-	props: Object;
+	props: { children?: ComponentChildren };
 	/**
 	 * Virtual node representing the element.
 	 */
-	element: VNode;
+	element: VNode< {
+		class?: string;
+		style?: string | Record< string, string | number >;
+	} >;
 	/**
 	 * The inherited context.
 	 */
@@ -52,7 +56,7 @@ interface DirectiveArgs {
 }
 
 interface DirectiveCallback {
-	( args: DirectiveArgs ): VNode | void;
+	( args: DirectiveArgs ): VNode | null;
 }
 
 interface DirectiveOptions {

From 29e2577963d6fd0ee4a5fdb62f68841acdd2e4b5 Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 18:11:32 +0200
Subject: [PATCH 06/14] types

---
 packages/interactivity/src/directives.tsx | 18 ++++++++++++------
 packages/interactivity/src/hooks.tsx      |  5 +++--
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/packages/interactivity/src/directives.tsx b/packages/interactivity/src/directives.tsx
index e2a118e163e17a..8e8e783ae125cb 100644
--- a/packages/interactivity/src/directives.tsx
+++ b/packages/interactivity/src/directives.tsx
@@ -8,7 +8,7 @@
  */
 import { h as createElement, type RefObject } from 'preact';
 import { useContext, useMemo, useRef } from 'preact/hooks';
-import { deepSignal, peek } from 'deepsignal';
+import { deepSignal, peek, type DeepSignal } from 'deepsignal';
 
 /**
  * Internal dependencies
@@ -49,7 +49,7 @@ const proxifyContext = ( current: object, inherited: object = {} ): object => {
 	contextObjectToFallback.set( current, inherited );
 	if ( ! contextObjectToProxy.has( current ) ) {
 		const proxy = new Proxy( current, {
-			get: ( target, k ) => {
+			get: ( target: DeepSignal< any >, k ) => {
 				const fallback = contextObjectToFallback.get( current );
 				// Always subscribe to prop changes in the current context.
 				const currentProp = target[ k ];
@@ -130,9 +130,12 @@ const proxifyContext = ( current: object, inherited: object = {} ): object => {
  * Recursively update values within a deepSignal object.
  *
  * @param target A deepSignal instance.
- * @param source Object with properties to update in `target`
+ * @param source Object with properties to update in `target`.
  */
-const updateSignals = ( target: object, source: object ) => {
+const updateSignals = (
+	target: DeepSignal< any >,
+	source: DeepSignal< any >
+) => {
 	for ( const k in source ) {
 		if (
 			isPlainObject( peek( target, k ) ) &&
@@ -181,7 +184,9 @@ const empty = ' ';
  * @param val CSS string.
  * @return CSS object.
  */
-const cssStringToObject = ( val: string ): object => {
+const cssStringToObject = (
+	val: string
+): Record< string, string | number > => {
 	const tree = [ {} ];
 	let block, left;
 
@@ -449,6 +454,8 @@ export default () => {
 				type: Type,
 				props: { innerHTML, ...rest },
 			},
+		}: {
+			element: any;
 		} ) => {
 			// Preserve the initial inner HTML.
 			const cached = useMemo( () => innerHTML, [] );
@@ -487,7 +494,6 @@ export default () => {
 			element,
 			evaluate,
 		} ) => {
-			// @ts-expect-error: template type is currently missing https://github.com/preactjs/preact/pull/4334
 			if ( element.type !== 'template' ) return;
 
 			const { Provider } = inheritedContext;
diff --git a/packages/interactivity/src/hooks.tsx b/packages/interactivity/src/hooks.tsx
index be7a053ec90081..ff8b8180557f93 100644
--- a/packages/interactivity/src/hooks.tsx
+++ b/packages/interactivity/src/hooks.tsx
@@ -43,6 +43,7 @@ interface DirectiveArgs {
 	element: VNode< {
 		class?: string;
 		style?: string | Record< string, string | number >;
+		content?: ComponentChildren;
 	} >;
 	/**
 	 * The inherited context.
@@ -56,7 +57,7 @@ interface DirectiveArgs {
 }
 
 interface DirectiveCallback {
-	( args: DirectiveArgs ): VNode | null;
+	( args: DirectiveArgs ): VNode | null | void;
 }
 
 interface DirectiveOptions {
@@ -71,7 +72,7 @@ interface DirectiveOptions {
 
 interface Scope {
 	evaluate: Evaluate;
-	context: Context< any >;
+	context?: object;
 	ref: RefObject< HTMLElement >;
 	attributes: createElement.JSX.HTMLAttributes;
 }

From 566b9fb5518c7ea057e4d8c97e920b1aa3b53af6 Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 18:13:14 +0200
Subject: [PATCH 07/14] =?UTF-8?q?stricter=E2=80=A6?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 packages/interactivity/tsconfig.json | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/packages/interactivity/tsconfig.json b/packages/interactivity/tsconfig.json
index 445fce42e73e54..ef79d9873e1989 100644
--- a/packages/interactivity/tsconfig.json
+++ b/packages/interactivity/tsconfig.json
@@ -5,14 +5,11 @@
 		"rootDir": "src",
 		"declarationDir": "build-types",
 
-		"alwaysStrict": false,
 		"strictNullChecks": false,
-		"strictBindCallApply": false,
-		"strictFunctionTypes": false,
 		"strictPropertyInitialization": false,
-		"noImplicitAny": false,
+
 		"noImplicitThis": false,
-		"useUnknownInCatchVariables": false
+		"noImplicitAny": false
 	},
 	"include": [ "src/**/*" ]
 }

From 14383bf7cedf233a2893f82d8427ba17fbafc49a Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 18:15:43 +0200
Subject: [PATCH 08/14] implicit this

---
 packages/interactivity/src/utils.ts  | 2 +-
 packages/interactivity/tsconfig.json | 1 -
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/packages/interactivity/src/utils.ts b/packages/interactivity/src/utils.ts
index e9162f0dd7cd79..8b6da05b938447 100644
--- a/packages/interactivity/src/utils.ts
+++ b/packages/interactivity/src/utils.ts
@@ -63,7 +63,7 @@ const afterNextFrame = ( callback: () => void ) => {
  */
 function createFlusher( compute: () => unknown, notify: () => void ): Flusher {
 	let flush: () => void;
-	const dispose = effect( function () {
+	const dispose = effect( function ( this: any ) {
 		flush = this.c.bind( this );
 		this.x = compute;
 		this.c = notify;
diff --git a/packages/interactivity/tsconfig.json b/packages/interactivity/tsconfig.json
index ef79d9873e1989..d991e2e56a9084 100644
--- a/packages/interactivity/tsconfig.json
+++ b/packages/interactivity/tsconfig.json
@@ -8,7 +8,6 @@
 		"strictNullChecks": false,
 		"strictPropertyInitialization": false,
 
-		"noImplicitThis": false,
 		"noImplicitAny": false
 	},
 	"include": [ "src/**/*" ]

From 81fc1f38abdfb607d21f55e89c0ae57d3364eabd Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 19:17:42 +0200
Subject: [PATCH 09/14] strict nulls

---
 packages/interactivity/src/vdom.ts   | 78 +++++++++++++++++++---------
 packages/interactivity/tsconfig.json |  1 -
 2 files changed, 54 insertions(+), 25 deletions(-)

diff --git a/packages/interactivity/src/vdom.ts b/packages/interactivity/src/vdom.ts
index 5a997993668094..2ab176b7acf0dc 100644
--- a/packages/interactivity/src/vdom.ts
+++ b/packages/interactivity/src/vdom.ts
@@ -1,16 +1,18 @@
 /**
  * External dependencies
  */
-import { h } from 'preact';
+import { h, type VNode, type JSX } from 'preact';
 /**
  * Internal dependencies
  */
 import { directivePrefix as p } from './constants';
 
+type TreeWalkerReturn = string | Node | VNode< any > | null;
+
 const ignoreAttr = `data-${ p }-ignore`;
 const islandAttr = `data-${ p }-interactive`;
 const fullPrefix = `data-${ p }-`;
-const namespaces = [];
+const namespaces: Array< string > = [];
 const currentNamespace = () => namespaces[ namespaces.length - 1 ] ?? null;
 
 // Regular expression for directive parsing.
@@ -38,33 +40,49 @@ export const hydratedIslands = new WeakSet();
 /**
  * Recursive function that transforms a DOM tree into vDOM.
  *
- * @param {Node} root The root element or node to start traversing on.
- * @return {import('preact').VNode[]} The resulting vDOM tree.
+ * @param root The root element or node to start traversing on.
+ * @return The resulting vDOM tree.
  */
-export function toVdom( root ) {
+export function toVdom( root: Node ): [ string | VNode | null, Node | null ] {
 	const treeWalker = document.createTreeWalker(
 		root,
 		205 // ELEMENT + TEXT + COMMENT + CDATA_SECTION + PROCESSING_INSTRUCTION
 	);
 
-	function walk( node ) {
-		const { attributes, nodeType, localName } = node;
+	function walk( node: Node ): [ string | VNode | null, Node | null ] {
+		const { nodeType } = node;
+
+		// TEXT_NODE (3)
+		if ( nodeType === 3 ) {
+			return [ ( node as Text ).data, null ];
+		}
 
-		if ( nodeType === 3 ) return [ node.data ];
+		// CDATA_SECTION_NODE (4)
 		if ( nodeType === 4 ) {
 			const next = treeWalker.nextSibling();
-			node.replaceWith( new window.Text( node.nodeValue ) );
+			( node as CDATASection ).replaceWith(
+				new window.Text( ( node as CDATASection ).nodeValue ?? '' )
+			);
 			return [ node.nodeValue, next ];
 		}
+
+		// COMMENT_NODE (8) || PROCESSING_INSTRUCTION_NODE (7)
 		if ( nodeType === 8 || nodeType === 7 ) {
 			const next = treeWalker.nextSibling();
-			node.remove();
+			( node as Comment | ProcessingInstruction ).remove();
 			return [ null, next ];
 		}
 
+		const elementNode = node as HTMLElement;
+
+		const attributes = elementNode.attributes;
+		const localName = elementNode.localName as keyof JSX.IntrinsicElements;
+
 		const props: Record< string, any > = {};
-		const children = [];
-		const directives = [];
+		const children: Array< TreeWalkerReturn > = [];
+		const directives: Array<
+			[ name: string, namespace: string | null, value: unknown ]
+		> = [];
 		let ignore = false;
 		let island = false;
 
@@ -81,7 +99,7 @@ export function toVdom( root ) {
 						.exec( attributes[ i ].value )
 						?.slice( 1 ) ?? [ null, attributes[ i ].value ];
 					try {
-						value = JSON.parse( value );
+						value = JSON.parse( value as string );
 					} catch ( e ) {}
 					if ( n === islandAttr ) {
 						island = true;
@@ -100,22 +118,29 @@ export function toVdom( root ) {
 			props[ n ] = attributes[ i ].value;
 		}
 
-		if ( ignore && ! island )
+		if ( ignore && ! island ) {
 			return [
-				h( localName, {
+				h< any, any >( localName, {
 					...props,
-					innerHTML: node.innerHTML,
+					innerHTML: elementNode.innerHTML,
 					__directives: { ignore: true },
 				} ),
+				null,
 			];
-		if ( island ) hydratedIslands.add( node );
+		}
+
+		if ( island ) {
+			hydratedIslands.add( elementNode );
+		}
 
 		if ( directives.length ) {
 			props.__directives = directives.reduce(
 				( obj, [ name, ns, value ] ) => {
 					const [ , prefix, suffix = 'default' ] =
-						directiveParser.exec( name );
+						directiveParser.exec( name )!;
+
 					if ( ! obj[ prefix ] ) obj[ prefix ] = [];
+
 					obj[ prefix ].push( {
 						namespace: ns ?? currentNamespace(),
 						value,
@@ -127,16 +152,19 @@ export function toVdom( root ) {
 			);
 		}
 
+		// @ts-expect-error Fixed in upcoming preact release https://github.com/preactjs/preact/pull/4334
 		if ( localName === 'template' ) {
-			props.content = [ ...node.content.childNodes ].map( ( childNode ) =>
-				toVdom( childNode )
-			);
+			props.content = [
+				...( elementNode as HTMLTemplateElement ).content.childNodes,
+			].map( ( childNode ) => toVdom( childNode ) );
 		} else {
 			let child = treeWalker.firstChild();
 			if ( child ) {
 				while ( child ) {
 					const [ vnode, nextChild ] = walk( child );
-					if ( vnode ) children.push( vnode );
+					if ( vnode ) {
+						children.push( vnode );
+					}
 					child = nextChild || treeWalker.nextSibling();
 				}
 				treeWalker.parentNode();
@@ -144,9 +172,11 @@ export function toVdom( root ) {
 		}
 
 		// Restore previous namespace.
-		if ( island ) namespaces.pop();
+		if ( island ) {
+			namespaces.pop();
+		}
 
-		return [ h( localName, props, children ) ];
+		return [ h( localName, props, children ), null ];
 	}
 
 	return walk( treeWalker.currentNode );
diff --git a/packages/interactivity/tsconfig.json b/packages/interactivity/tsconfig.json
index d991e2e56a9084..bd921d194888ac 100644
--- a/packages/interactivity/tsconfig.json
+++ b/packages/interactivity/tsconfig.json
@@ -5,7 +5,6 @@
 		"rootDir": "src",
 		"declarationDir": "build-types",
 
-		"strictNullChecks": false,
 		"strictPropertyInitialization": false,
 
 		"noImplicitAny": false

From 7c9afc55a28194be0879bc99f573ff842ad0c86b Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 19:20:38 +0200
Subject: [PATCH 10/14] handle not found text entry

---
 packages/interactivity/src/directives.tsx | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/packages/interactivity/src/directives.tsx b/packages/interactivity/src/directives.tsx
index 8e8e783ae125cb..42e07f60e0bf58 100644
--- a/packages/interactivity/src/directives.tsx
+++ b/packages/interactivity/src/directives.tsx
@@ -471,6 +471,11 @@ export default () => {
 	// data-wp-text
 	directive( 'text', ( { directives: { text }, element, evaluate } ) => {
 		const entry = text.find( ( { suffix } ) => suffix === 'default' );
+		if ( ! entry ) {
+			element.props.children = null;
+			return;
+		}
+
 		try {
 			const result = evaluate( entry );
 			element.props.children =

From dabad8f4220fb2f181af24053e1a39909bd64e42 Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 19:25:57 +0200
Subject: [PATCH 11/14] hooks

---
 packages/interactivity/src/utils.ts | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/interactivity/src/utils.ts b/packages/interactivity/src/utils.ts
index 8b6da05b938447..6919575e97bd3b 100644
--- a/packages/interactivity/src/utils.ts
+++ b/packages/interactivity/src/utils.ts
@@ -62,7 +62,7 @@ const afterNextFrame = ( callback: () => void ) => {
  * @return The Flusher object with `flush` and `dispose` properties.
  */
 function createFlusher( compute: () => unknown, notify: () => void ): Flusher {
-	let flush: () => void;
+	let flush: () => void = () => undefined;
 	const dispose = effect( function ( this: any ) {
 		flush = this.c.bind( this );
 		this.x = compute;
@@ -82,7 +82,7 @@ function createFlusher( compute: () => unknown, notify: () => void ): Flusher {
  */
 export function useSignalEffect( callback: () => unknown ) {
 	_useEffect( () => {
-		let eff = null;
+		let eff: Flusher | null = null;
 		let isExecuting = false;
 
 		const notify = async () => {
@@ -271,7 +271,7 @@ export const createRootFragment = (
 	parent: Element,
 	replaceNode: Node | Node[]
 ) => {
-	replaceNode = [].concat( replaceNode );
+	replaceNode = ( [] as Node[] ).concat( replaceNode );
 	const sibling = replaceNode[ replaceNode.length - 1 ].nextSibling;
 	function insert( child: any, root: any ) {
 		parent.insertBefore( child, root || sibling );

From 31fcd3da73559b9b43cac1cf04000e485260f7c6 Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 19:27:11 +0200
Subject: [PATCH 12/14] store

---
 packages/interactivity/src/store.ts | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/interactivity/src/store.ts b/packages/interactivity/src/store.ts
index 2aad8c23d1db12..ff70b4ab297085 100644
--- a/packages/interactivity/src/store.ts
+++ b/packages/interactivity/src/store.ts
@@ -17,7 +17,7 @@ import {
 } from './hooks';
 
 const isObject = ( item: unknown ): item is Record< string, unknown > =>
-	item && typeof item === 'object' && item.constructor === Object;
+	Boolean( item && typeof item === 'object' && item.constructor === Object );
 
 const deepMerge = ( target: any, source: any ) => {
 	if ( isObject( target ) && isObject( source ) ) {
@@ -332,12 +332,12 @@ export const populateInitialData = ( data?: {
 	config?: Record< string, unknown >;
 } ) => {
 	if ( isObject( data?.state ) ) {
-		Object.entries( data.state ).forEach( ( [ namespace, state ] ) => {
+		Object.entries( data!.state ).forEach( ( [ namespace, state ] ) => {
 			store( namespace, { state }, { lock: universalUnlock } );
 		} );
 	}
 	if ( isObject( data?.config ) ) {
-		Object.entries( data.config ).forEach( ( [ namespace, config ] ) => {
+		Object.entries( data!.config ).forEach( ( [ namespace, config ] ) => {
 			storeConfigs.set( namespace, config );
 		} );
 	}

From 44c93217e9506440bfcb535add911f2c75ab87c0 Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 19:29:49 +0200
Subject: [PATCH 13/14] Scope

---
 packages/interactivity/src/hooks.tsx | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/interactivity/src/hooks.tsx b/packages/interactivity/src/hooks.tsx
index ff8b8180557f93..39be45ecd94ada 100644
--- a/packages/interactivity/src/hooks.tsx
+++ b/packages/interactivity/src/hooks.tsx
@@ -72,7 +72,7 @@ interface DirectiveOptions {
 
 interface Scope {
 	evaluate: Evaluate;
-	context?: object;
+	context: object;
 	ref: RefObject< HTMLElement >;
 	attributes: createElement.JSX.HTMLAttributes;
 }

From 65491b9fe897d7a37db51470b4dadfcb0e1c5c2a Mon Sep 17 00:00:00 2001
From: Jon Surrell <sirreal@users.noreply.github.com>
Date: Wed, 10 Apr 2024 19:31:49 +0200
Subject: [PATCH 14/14] I hate it

---
 packages/interactivity/src/vdom.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/interactivity/src/vdom.ts b/packages/interactivity/src/vdom.ts
index 2ab176b7acf0dc..692fd0dffea27d 100644
--- a/packages/interactivity/src/vdom.ts
+++ b/packages/interactivity/src/vdom.ts
@@ -106,7 +106,7 @@ export function toVdom( root: Node ): [ string | VNode | null, Node | null ] {
 						namespaces.push(
 							typeof value === 'string'
 								? value
-								: value?.namespace ?? null
+								: ( value as any )?.namespace ?? null
 						);
 					} else {
 						directives.push( [ n, ns, value ] );