diff --git a/src/core/index.ts b/src/core/index.ts
index 86793380..7b871fa8 100644
--- a/src/core/index.ts
+++ b/src/core/index.ts
@@ -6,4 +6,4 @@ export type {
   AnimatableCSSProperties,
   PlayOptions,
   WaitingAnimationEventName,
-} from "./waapi";
+} from "./waapi.js";
diff --git a/src/core/utils.spec.ts b/src/core/utils.spec.ts
index c24c1e09..e3d45591 100644
--- a/src/core/utils.spec.ts
+++ b/src/core/utils.spec.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect } from "vitest";
-import { isSameObject, isSameObjectArray } from "./utils";
+import { isSameObject, isSameObjectArray } from "./utils.js";
 
 describe("isSameObject", () => {
   it("should return true if the objects are same", () => {
diff --git a/src/core/waapi.spec.ts b/src/core/waapi.spec.ts
index 21fa610b..97df104e 100644
--- a/src/core/waapi.spec.ts
+++ b/src/core/waapi.spec.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect } from "vitest";
-import { getKeyframeKeys } from "./waapi";
+import { getKeyframeKeys } from "./waapi.js";
 
 describe("getKeyframeKeys", () => {
   it("normal", () => {
diff --git a/src/core/waapi.ts b/src/core/waapi.ts
index aae791f4..b9ddf0b2 100644
--- a/src/core/waapi.ts
+++ b/src/core/waapi.ts
@@ -1,5 +1,5 @@
 import type { CSSProperties } from "react";
-import { getKeys, uniq } from "./utils";
+import { getKeys, uniq } from "./utils.js";
 
 export type AnimatableCSSProperties = Omit<
   CSSProperties,
diff --git a/src/index.ts b/src/index.ts
index c8fe1353..bcafe77b 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,2 +1,2 @@
-export * from "./core";
-export * from "./react";
+export * from "./core/index.js";
+export * from "./react/index.js";
diff --git a/src/react/components/TransitionGroup.tsx b/src/react/components/TransitionGroup.tsx
index 203642da..07271e6f 100644
--- a/src/react/components/TransitionGroup.tsx
+++ b/src/react/components/TransitionGroup.tsx
@@ -8,7 +8,7 @@ import {
   ReactElement,
   useCallback,
 } from "react";
-import { noop } from "../../core/utils";
+import { noop } from "../../core/utils.js";
 
 const toMap = (elements: ReactElement[]) =>
   elements.reduce((acc, e, i) => {
diff --git a/src/react/components/index.ts b/src/react/components/index.ts
index 47a47d24..62e0176f 100644
--- a/src/react/components/index.ts
+++ b/src/react/components/index.ts
@@ -1,2 +1,2 @@
-export { TransitionGroup } from "./TransitionGroup";
-export type { TransitionGroupProps } from "./TransitionGroup";
+export { TransitionGroup } from "./TransitionGroup.js";
+export type { TransitionGroupProps } from "./TransitionGroup.js";
diff --git a/src/react/hooks/index.ts b/src/react/hooks/index.ts
index 83ec9131..7e987544 100644
--- a/src/react/hooks/index.ts
+++ b/src/react/hooks/index.ts
@@ -1,5 +1,5 @@
-export * from "./useAnimation";
-export * from "./useAnimationFunction";
-export * from "./useTransitionAnimation";
-export * from "./useScrollTimeline";
-export * from "./useViewTimeline";
+export * from "./useAnimation.js";
+export * from "./useAnimationFunction.js";
+export * from "./useTransitionAnimation.js";
+export * from "./useScrollTimeline.js";
+export * from "./useViewTimeline.js";
diff --git a/src/react/hooks/state.ts b/src/react/hooks/state.ts
index a4ea3c1f..aaa0c4b0 100644
--- a/src/react/hooks/state.ts
+++ b/src/react/hooks/state.ts
@@ -1,5 +1,5 @@
-import { isSameObject, isSameObjectArray } from "../../core/utils";
-import { createAnimation } from "../../core/waapi";
+import { isSameObject, isSameObjectArray } from "../../core/utils.js";
+import { createAnimation } from "../../core/waapi.js";
 
 /**
  * @internal
diff --git a/src/react/hooks/useAnimation.ssr.spec.tsx b/src/react/hooks/useAnimation.ssr.spec.tsx
index baca99f0..0a06654c 100644
--- a/src/react/hooks/useAnimation.ssr.spec.tsx
+++ b/src/react/hooks/useAnimation.ssr.spec.tsx
@@ -4,7 +4,7 @@
 import { it, describe, expect } from "vitest";
 import { useEffect } from "react";
 import { renderToString, renderToStaticMarkup } from "react-dom/server";
-import { useAnimation } from "./useAnimation";
+import { useAnimation } from "./useAnimation.js";
 
 describe("SSR", () => {
   const Comp = () => {
diff --git a/src/react/hooks/useAnimation.ts b/src/react/hooks/useAnimation.ts
index 93d83aa6..02622779 100644
--- a/src/react/hooks/useAnimation.ts
+++ b/src/react/hooks/useAnimation.ts
@@ -1,5 +1,5 @@
 import { useEffect } from "react";
-import { assign, getStyle, toArray } from "../../core/utils";
+import { assign, getStyle, toArray } from "../../core/utils.js";
 import {
   PlayOptions,
   _cancel,
@@ -13,16 +13,16 @@ import {
   WaitingAnimationEventName,
   TypedKeyframe,
   GetKeyframeFunction,
-} from "../../core/waapi";
-import { useStatic } from "./useStatic";
-import { useLatestRef } from "./useLatestRef";
-import { AnimationDefinition } from "../types";
+} from "../../core/waapi.js";
+import { useStatic } from "./useStatic.js";
+import { useLatestRef } from "./useLatestRef.js";
+import { AnimationDefinition } from "../types/index.js";
 import {
   deleteAnimation,
   getAnimation,
   AnimationObject,
   initAnimation,
-} from "./state";
+} from "./state.js";
 
 const normalizeKeyframe = <Args>(
   el: Element,
diff --git a/src/react/hooks/useAnimationFunction.ssr.spec.tsx b/src/react/hooks/useAnimationFunction.ssr.spec.tsx
index f56f16c5..6273071c 100644
--- a/src/react/hooks/useAnimationFunction.ssr.spec.tsx
+++ b/src/react/hooks/useAnimationFunction.ssr.spec.tsx
@@ -7,7 +7,7 @@ import { renderToString, renderToStaticMarkup } from "react-dom/server";
 import {
   useAnimationFunction,
   ComputedTimingContext,
-} from "./useAnimationFunction";
+} from "./useAnimationFunction.js";
 
 describe("SSR", () => {
   const Comp = () => {
diff --git a/src/react/hooks/useAnimationFunction.ts b/src/react/hooks/useAnimationFunction.ts
index 590b8ad6..ab603c3f 100644
--- a/src/react/hooks/useAnimationFunction.ts
+++ b/src/react/hooks/useAnimationFunction.ts
@@ -1,5 +1,5 @@
 import { useEffect } from "react";
-import { isSameObject } from "../../core/utils";
+import { isSameObject } from "../../core/utils.js";
 import {
   TypedKeyframeEffectOptions,
   createAnimation,
@@ -12,10 +12,10 @@ import {
   _setRate,
   _setTime,
   WaitingAnimationEventName,
-} from "../../core/waapi";
-import type { BaseAnimationHandle } from "./useAnimation";
-import { useStatic } from "./useStatic";
-import { useLatestRef } from "./useLatestRef";
+} from "../../core/waapi.js";
+import type { BaseAnimationHandle } from "./useAnimation.js";
+import { useStatic } from "./useStatic.js";
+import { useLatestRef } from "./useLatestRef.js";
 
 /**
  * Handle of {@link useAnimationFunction}.
diff --git a/src/react/hooks/useLatestRef.ts b/src/react/hooks/useLatestRef.ts
index 8af38acf..31fd6b59 100644
--- a/src/react/hooks/useLatestRef.ts
+++ b/src/react/hooks/useLatestRef.ts
@@ -1,5 +1,5 @@
 import { useRef } from "react";
-import { useIsomorphicLayoutEffect } from "./useIsomorphicLayoutEffect";
+import { useIsomorphicLayoutEffect } from "./useIsomorphicLayoutEffect.js";
 
 /**
  * @internal
diff --git a/src/react/hooks/useScrollTimeline.ts b/src/react/hooks/useScrollTimeline.ts
index da0e5c12..b7a78bcc 100644
--- a/src/react/hooks/useScrollTimeline.ts
+++ b/src/react/hooks/useScrollTimeline.ts
@@ -1,8 +1,8 @@
-import { assign } from "../../core/utils";
-import { ScrollTimelineAxis, TimelineDefinition } from "../types";
-import { SCROLL_TIMELINE } from "../types/internal";
-import { useLatestRef } from "./useLatestRef";
-import { useStatic } from "./useStatic";
+import { assign } from "../../core/utils.js";
+import { ScrollTimelineAxis, TimelineDefinition } from "../types/index.js";
+import { SCROLL_TIMELINE } from "../types/internal.js";
+import { useLatestRef } from "./useLatestRef.js";
+import { useStatic } from "./useStatic.js";
 
 export interface ScrollTimelineOpts {
   axis?: ScrollTimelineAxis;
diff --git a/src/react/hooks/useTransitionAnimation.ts b/src/react/hooks/useTransitionAnimation.ts
index c6db4045..9d960249 100644
--- a/src/react/hooks/useTransitionAnimation.ts
+++ b/src/react/hooks/useTransitionAnimation.ts
@@ -6,17 +6,17 @@ import {
   TransitionNotifierContext,
   TransitionState,
   TransitionStateContext,
-} from "../components/TransitionGroup";
-import { AnimationHandle, useAnimation } from "./useAnimation";
-import { getKeys, noop } from "../../core/utils";
-import { useIsomorphicLayoutEffect } from "./useIsomorphicLayoutEffect";
+} from "../components/TransitionGroup.js";
+import { AnimationHandle, useAnimation } from "./useAnimation.js";
+import { getKeys, noop } from "../../core/utils.js";
+import { useIsomorphicLayoutEffect } from "./useIsomorphicLayoutEffect.js";
 import type {
   TypedKeyframeEffectOptions,
   GetKeyframeFunction,
   TypedKeyframe,
-} from "../../core";
-import { useStatic } from "./useStatic";
-import { useLatestRef } from "./useLatestRef";
+} from "../../core/index.js";
+import { useStatic } from "./useStatic.js";
+import { useLatestRef } from "./useLatestRef.js";
 
 export interface TransitionAnimationHandle {
   (ref: Element | null): void;
diff --git a/src/react/hooks/useViewTimeline.ts b/src/react/hooks/useViewTimeline.ts
index 931651db..a958580e 100644
--- a/src/react/hooks/useViewTimeline.ts
+++ b/src/react/hooks/useViewTimeline.ts
@@ -1,12 +1,12 @@
-import { assign } from "../../core/utils";
+import { assign } from "../../core/utils.js";
 import {
   ScrollTimelineAxis,
   TimelineDefinition,
   ViewTimelineInset,
-} from "../types";
-import { VIEW_TIMELINE } from "../types/internal";
-import { useLatestRef } from "./useLatestRef";
-import { useStatic } from "./useStatic";
+} from "../types/index.js";
+import { VIEW_TIMELINE } from "../types/internal.js";
+import { useLatestRef } from "./useLatestRef.js";
+import { useStatic } from "./useStatic.js";
 
 export interface ViewTimelineOpts {
   axis?: ScrollTimelineAxis;
diff --git a/src/react/index.ts b/src/react/index.ts
index 777db88c..910f93f1 100644
--- a/src/react/index.ts
+++ b/src/react/index.ts
@@ -1,3 +1,3 @@
-export * from "./components";
-export * from "./hooks";
-export * from "./types";
+export * from "./components/index.js";
+export * from "./hooks/index.js";
+export * from "./types/index.js";
diff --git a/src/react/types/index.ts b/src/react/types/index.ts
index 87a560be..5e690abb 100644
--- a/src/react/types/index.ts
+++ b/src/react/types/index.ts
@@ -2,8 +2,8 @@ import {
   GetKeyframeFunction,
   TypedKeyframe,
   TypedKeyframeEffectOptions,
-} from "../../core";
-import { SCROLL_TIMELINE, VIEW_TIMELINE } from "./internal";
+} from "../../core/index.js";
+import { SCROLL_TIMELINE, VIEW_TIMELINE } from "./internal.js";
 
 export interface AnimationOptions extends TypedKeyframeEffectOptions {
   timeline?: TimelineDefinition;
diff --git a/tsconfig.json b/tsconfig.json
index 90971cde..a730ce26 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,8 +1,8 @@
 {
   "compilerOptions": {
     "target": "es2018",
-    "module": "esnext",
-    "moduleResolution": "bundler",
+    "module": "nodenext",
+    "moduleResolution": "nodenext",
     "jsx": "react-jsx",
     "lib": ["dom", "dom.iterable", "esnext"],
     "strict": true,