diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/create-extension-class.function.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/create-extension-class.function.ts
index 45b7fde848..b772ec80f5 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/create-extension-class.function.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/create-extension-class.function.ts
@@ -1,7 +1,7 @@
-import { hasDefaultExport } from './has-default-export.function';
-import { isManifestClassConstructorType } from './type-guards';
-import { loadExtension } from './load-extension.function';
-import type { ManifestClass, ClassConstructor } from './types';
+import { hasDefaultExport } from './has-default-export.function.js';
+import { isManifestClassConstructorType } from './type-guards/index.js';
+import { loadExtension } from './load-extension.function.js';
+import type { ManifestClass, ClassConstructor } from './types.js';
 
 //TODO: Write tests for this method:
 export async function createExtensionClass<T = unknown>(
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/create-extension-element-or-fallback.function.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/create-extension-element-or-fallback.function.ts
index 19fae25b4f..97760bd252 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/create-extension-element-or-fallback.function.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/create-extension-element-or-fallback.function.ts
@@ -1,5 +1,5 @@
-import { createExtensionElement } from './create-extension-element.function';
-import { isManifestElementableType } from './type-guards';
+import { createExtensionElement } from './create-extension-element.function.js';
+import { isManifestElementableType } from './type-guards/index.js';
 
 export async function createExtensionElementOrFallback(
 	manifest: any,
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/create-extension-element.function.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/create-extension-element.function.ts
index 07a282bac4..d781554d59 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/create-extension-element.function.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/create-extension-element.function.ts
@@ -1,7 +1,7 @@
-import { hasDefaultExport } from './has-default-export.function';
-import { isManifestElementNameType } from './type-guards';
-import { loadExtension } from './load-extension.function';
-import type { HTMLElementConstructor, ManifestElement } from './types';
+import { hasDefaultExport } from './has-default-export.function.js';
+import { isManifestElementNameType } from './type-guards/index.js';
+import { loadExtension } from './load-extension.function.js';
+import type { HTMLElementConstructor, ManifestElement } from './types.js';
 
 export async function createExtensionElement<ElementType extends HTMLElement>(
 	manifest: ManifestElement<ElementType>
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/entry-point-extension-initializer.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/entry-point-extension-initializer.ts
index d3b9f6ed96..fe5bbfa414 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/entry-point-extension-initializer.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/entry-point-extension-initializer.ts
@@ -1,7 +1,7 @@
-import type { ManifestEntryPoint } from './types';
-import { hasInitExport } from './has-init-export.function';
-import { loadExtension } from './load-extension.function';
-import { UmbExtensionRegistry } from './registry/extension.registry';
+import type { ManifestEntryPoint } from './types.js';
+import { hasInitExport } from './has-init-export.function.js';
+import { loadExtension } from './load-extension.function.js';
+import { UmbExtensionRegistry } from './registry/extension.registry.js';
 import { UmbControllerHostElement } from '@umbraco-cms/backoffice/controller-api';
 
 export class UmbEntryPointExtensionInitializer {
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/has-init-export.function.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/has-init-export.function.ts
index abcc3c9095..585b76ee99 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/has-init-export.function.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/has-init-export.function.ts
@@ -1,4 +1,4 @@
-import type { UmbEntryPointModule } from './umb-lifecycle.interface';
+import type { UmbEntryPointModule } from './umb-lifecycle.interface.js';
 
 /**
  * Validate if an ESModule exports a known init function called 'onInit'
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/index.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/index.ts
index 9370b946d0..b1b67865e7 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/index.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/index.ts
@@ -1,11 +1,11 @@
-export * from './registry/extension.registry';
-export * from './type-guards';
-export * from './create-extension-element.function';
-export * from './has-default-export.function';
-export * from './has-init-export.function';
-export * from './load-extension.function';
-export * from './create-extension-element-or-fallback.function';
-export * from './create-extension-class.function';
-export * from './umb-lifecycle.interface';
-export * from './entry-point-extension-initializer';
-export * from './types';
+export * from './registry/extension.registry.js';
+export * from './type-guards/index.js';
+export * from './create-extension-element.function.js';
+export * from './has-default-export.function.js';
+export * from './has-init-export.function.js';
+export * from './load-extension.function.js';
+export * from './create-extension-element-or-fallback.function.js';
+export * from './create-extension-class.function.js';
+export * from './umb-lifecycle.interface.js';
+export * from './entry-point-extension-initializer.js';
+export * from './types.js';
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/load-extension.function.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/load-extension.function.ts
index 75d9615ffe..1607d396a9 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/load-extension.function.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/load-extension.function.ts
@@ -1,5 +1,5 @@
-import { isManifestJSType, isManifestLoaderType } from './type-guards';
-import type { ManifestWithLoader } from './types';
+import { isManifestJSType, isManifestLoaderType } from './type-guards/index.js';
+import type { ManifestWithLoader } from './types.js';
 
 export async function loadExtension<T = unknown>(manifest: ManifestWithLoader<T>): Promise<T | null> {
 	try {
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/registry/extension.registry.test.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/registry/extension.registry.test.ts
index 477e41a54a..3901cab6ab 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/registry/extension.registry.test.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/registry/extension.registry.test.ts
@@ -1,6 +1,6 @@
 import { expect } from '@open-wc/testing';
-import type { ManifestElementWithElementName, ManifestKind, ManifestWithMeta } from '../types';
-import { UmbExtensionRegistry } from './extension.registry';
+import type { ManifestElementWithElementName, ManifestKind, ManifestWithMeta } from '../types.js';
+import { UmbExtensionRegistry } from './extension.registry.js';
 
 describe('UmbExtensionRegistry', () => {
 	let extensionRegistry: UmbExtensionRegistry<ManifestWithMeta>;
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/registry/extension.registry.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/registry/extension.registry.ts
index 5a454dc97a..e08b64c052 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/registry/extension.registry.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/registry/extension.registry.ts
@@ -1,5 +1,5 @@
 import { BehaviorSubject, map, Observable, distinctUntilChanged, combineLatest } from 'rxjs';
-import type { ManifestTypeMap, ManifestBase, SpecificManifestTypeOrManifestBase, ManifestKind } from '../types';
+import type { ManifestTypeMap, ManifestBase, SpecificManifestTypeOrManifestBase, ManifestKind } from '../types.js';
 
 function extensionArrayMemoization<T extends { alias: string }>(
 	previousValue: Array<T>,
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/index.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/index.ts
index a314097c9b..fb5cc49979 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/index.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/index.ts
@@ -1,6 +1,6 @@
-export * from './is-manifest-class-instance-type.function';
-export * from './is-manifest-classable-type.function';
-export * from './is-manifest-element-name-type.function';
-export * from './is-manifest-elementable-type.function';
-export * from './is-manifest-js-type.function';
-export * from './is-manifest-loader-type.function';
+export * from './is-manifest-class-instance-type.function.js';
+export * from './is-manifest-classable-type.function.js';
+export * from './is-manifest-element-name-type.function.js';
+export * from './is-manifest-elementable-type.function.js';
+export * from './is-manifest-js-type.function.js';
+export * from './is-manifest-loader-type.function.js';
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-class-instance-type.function.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-class-instance-type.function.ts
index 7472005e30..dc18c78b6b 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-class-instance-type.function.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-class-instance-type.function.ts
@@ -1,4 +1,4 @@
-import type { ManifestClass, ManifestClassWithClassConstructor } from '../types';
+import type { ManifestClass, ManifestClassWithClassConstructor } from '../types.js';
 
 export function isManifestClassConstructorType(manifest: unknown): manifest is ManifestClassWithClassConstructor {
 	return typeof manifest === 'object' && manifest !== null && (manifest as ManifestClass).class !== undefined;
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-classable-type.function.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-classable-type.function.ts
index 04913b5d29..b5e83c4ba4 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-classable-type.function.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-classable-type.function.ts
@@ -1,7 +1,7 @@
-import type { ManifestBase, ManifestClass } from '../types';
-import { isManifestJSType } from './is-manifest-js-type.function';
-import { isManifestLoaderType } from './is-manifest-loader-type.function';
-import { isManifestClassConstructorType } from './is-manifest-class-instance-type.function';
+import type { ManifestBase, ManifestClass } from '../types.js';
+import { isManifestJSType } from './is-manifest-js-type.function.js';
+import { isManifestLoaderType } from './is-manifest-loader-type.function.js';
+import { isManifestClassConstructorType } from './is-manifest-class-instance-type.function.js';
 
 export function isManifestClassableType(manifest: ManifestBase): manifest is ManifestClass {
 	return (
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-element-name-type.function.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-element-name-type.function.ts
index 2076793178..9c02956850 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-element-name-type.function.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-element-name-type.function.ts
@@ -1,4 +1,4 @@
-import type { ManifestElement, ManifestElementWithElementName } from '../types';
+import type { ManifestElement, ManifestElementWithElementName } from '../types.js';
 
 export function isManifestElementNameType(manifest: unknown): manifest is ManifestElementWithElementName {
 	return typeof manifest === 'object' && manifest !== null && (manifest as ManifestElement).elementName !== undefined;
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-elementable-type.function.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-elementable-type.function.ts
index f0643d92f2..01ab3ca8a7 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-elementable-type.function.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-elementable-type.function.ts
@@ -1,7 +1,7 @@
-import type { ManifestElement, ManifestBase } from '../types';
-import { isManifestElementNameType } from './is-manifest-element-name-type.function';
-import { isManifestJSType } from './is-manifest-js-type.function';
-import { isManifestLoaderType } from './is-manifest-loader-type.function';
+import type { ManifestElement, ManifestBase } from '../types.js';
+import { isManifestElementNameType } from './is-manifest-element-name-type.function.js';
+import { isManifestJSType } from './is-manifest-js-type.function.js';
+import { isManifestLoaderType } from './is-manifest-loader-type.function.js';
 
 export function isManifestElementableType<ElementType extends HTMLElement = HTMLElement>(
 	manifest: ManifestBase
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-js-type.function.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-js-type.function.ts
index 27e9aefb1f..5220d57f83 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-js-type.function.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-js-type.function.ts
@@ -1,4 +1,4 @@
-import type { ManifestBase, ManifestWithLoader } from '../types';
+import type { ManifestBase, ManifestWithLoader } from '../types.js';
 
 export type ManifestJSType<T> = ManifestWithLoader<T> & { js: string };
 export function isManifestJSType<T>(manifest: ManifestBase | unknown): manifest is ManifestJSType<T> {
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-loader-type.function.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-loader-type.function.ts
index 5ee9ef3411..bf607aa132 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-loader-type.function.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/type-guards/is-manifest-loader-type.function.ts
@@ -1,4 +1,4 @@
-import type { ManifestBase, ManifestWithLoader } from '../types';
+import type { ManifestBase, ManifestWithLoader } from '../types.js';
 
 export type ManifestLoaderType<T> = ManifestWithLoader<T> & {
 	loader: () => Promise<T>;
diff --git a/src/Umbraco.Web.UI.Client/src/libs/extension-api/umb-lifecycle.interface.ts b/src/Umbraco.Web.UI.Client/src/libs/extension-api/umb-lifecycle.interface.ts
index c2dd1f83a2..2057abf5f6 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/extension-api/umb-lifecycle.interface.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/extension-api/umb-lifecycle.interface.ts
@@ -1,5 +1,5 @@
-import type { UmbExtensionRegistry } from './registry/extension.registry';
-import { ManifestBase } from './types';
+import type { UmbExtensionRegistry } from './registry/extension.registry.js';
+import { ManifestBase } from './types.js';
 import type { UmbControllerHostElement } from '@umbraco-cms/backoffice/controller-api';
 
 export type UmbEntryPointOnInit = (