diff --git a/.github/workflows/test-javascript.yml b/.github/workflows/test-javascript.yml
index e1817828..b297d7f9 100644
--- a/.github/workflows/test-javascript.yml
+++ b/.github/workflows/test-javascript.yml
@@ -27,7 +27,7 @@ jobs:
       matrix:
         os:
           - ubuntu-latest
-        node-version: [22.x, 24.x]
+        node-version: [22.x, 24.x, 26.x]
         include:
           - os: windows-latest
             node-version: 22.x
@@ -60,7 +60,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        node-version: [22.x, 24.x]
+        node-version: [22.x, 24.x, 26.x]
 
     steps:
       - name: set git core.autocrlf to 'input'
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9547c470..12836117 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
+### Changed
+- BREAKING CHANGE: [JavaScript] Switch to ESM ([#513](https://github.com/cucumber/html-formatter/pull/513))
 
 ## [23.1.0] - 2026-04-13
 ### Changed
diff --git a/javascript/.mocharc.json b/javascript/.mocharc.json
index c929b6cc..d1690433 100644
--- a/javascript/.mocharc.json
+++ b/javascript/.mocharc.json
@@ -1,5 +1,5 @@
 {
-  "require": ["ts-node/register", "source-map-support/register"],
+  "node-option": ["loader=ts-node/esm", "require=source-map-support/register"],
   "spec": "src/**/*.spec.ts",
   "extension": ["ts", "tsx"],
   "recursive": true,
diff --git a/javascript/package.json b/javascript/package.json
index ba7aa299..1c151f87 100644
--- a/javascript/package.json
+++ b/javascript/package.json
@@ -2,6 +2,7 @@
   "name": "@cucumber/html-formatter",
   "version": "23.1.0",
   "description": "HTML formatter for Cucumber",
+  "type": "module",
   "main": "dist/src/index.js",
   "types": "dist/src/index.d.ts",
   "repository": {
@@ -15,6 +16,7 @@
     "build:tsc": "tsc --build tsconfig.build.json",
     "build:webpack": "webpack",
     "build": "npm run clean && npm run build:tsc && npm run prepare && npm run build:webpack",
+    "postbuild": "node -e \"require('.')\"",
     "prepare": "shx mkdir -p dist/src && shx cp src/*.scss dist/src && shx cp src/index.mustache dist/src && shx cp src/icon.url dist/src",
     "test": "mocha",
     "prepublishOnly": "npm run build",
diff --git a/javascript/src/CucumberHtmlStream.spec.ts b/javascript/src/CucumberHtmlStream.spec.ts
index 21bee1d5..14a4f939 100644
--- a/javascript/src/CucumberHtmlStream.spec.ts
+++ b/javascript/src/CucumberHtmlStream.spec.ts
@@ -2,7 +2,7 @@ import assert from 'node:assert'
 import { Writable } from 'node:stream'
 import type { Envelope } from '@cucumber/messages'
 
-import { CucumberHtmlStream } from './CucumberHtmlStream'
+import { CucumberHtmlStream } from './CucumberHtmlStream.js'
 
 async function renderAsHtml(...envelopes: Envelope[]): Promise<string> {
   return new Promise((resolve, reject) => {
@@ -15,8 +15,8 @@ async function renderAsHtml(...envelopes: Envelope[]): Promise<string> {
     })
     sink.on('finish', () => resolve(html))
     const cucumberHtmlStream = new CucumberHtmlStream(
-      `${__dirname}/dummy.css`,
-      `${__dirname}/dummy.js`
+      `${import.meta.dirname}/dummy.css`,
+      `${import.meta.dirname}/dummy.js`
     )
     cucumberHtmlStream.on('error', reject)
     cucumberHtmlStream.pipe(sink)
diff --git a/javascript/src/CucumberHtmlStream.ts b/javascript/src/CucumberHtmlStream.ts
index 91bdd9a8..84c1a468 100644
--- a/javascript/src/CucumberHtmlStream.ts
+++ b/javascript/src/CucumberHtmlStream.ts
@@ -15,9 +15,9 @@ export class CucumberHtmlStream extends Transform {
    * @param iconPath
    */
   constructor(
-    private readonly cssPath: string = path.join(__dirname, '..', 'main.css'),
-    private readonly jsPath: string = path.join(__dirname, '..', 'main.js'),
-    private readonly iconPath: string = path.join(__dirname, 'icon.url')
+    private readonly cssPath: string = path.join(import.meta.dirname, '..', 'main.css'),
+    private readonly jsPath: string = path.join(import.meta.dirname, '..', 'main.js'),
+    private readonly iconPath: string = path.join(import.meta.dirname, 'icon.url')
   ) {
     super({ objectMode: true })
   }
@@ -140,7 +140,7 @@ export class CucumberHtmlStream extends Transform {
     if (this.template !== null) {
       return callback(null, this.template)
     }
-    fs.readFile(`${__dirname}/index.mustache`, { encoding: 'utf-8' }, (err, template) => {
+    fs.readFile(`${import.meta.dirname}/index.mustache`, { encoding: 'utf-8' }, (err, template) => {
       if (err) {
         return callback(err)
       }
diff --git a/javascript/src/index.ts b/javascript/src/index.ts
index fd3544f6..eaa67059 100644
--- a/javascript/src/index.ts
+++ b/javascript/src/index.ts
@@ -1,6 +1,6 @@
-import { CucumberHtmlStream } from './CucumberHtmlStream'
+import { CucumberHtmlStream } from './CucumberHtmlStream.js'
 
-export * from './CucumberHtmlStream'
+export * from './CucumberHtmlStream.js'
 
 /**
  * @deprecated use the named export `CucumberHtmlStream` instead
diff --git a/javascript/test/acceptance.spec.ts b/javascript/test/acceptance.spec.ts
index 972fb284..133da159 100644
--- a/javascript/test/acceptance.spec.ts
+++ b/javascript/test/acceptance.spec.ts
@@ -6,12 +6,12 @@ import { NdjsonToMessageStream } from '@cucumber/message-streams'
 import { expect, test } from '@playwright/test'
 import { sync } from 'glob'
 
-import { CucumberHtmlStream } from '../src'
+import { CucumberHtmlStream } from '../src/index.js'
 
 const fixtures = sync(`./node_modules/@cucumber/compatibility-kit/features/**/*.ndjson`)
 
 test.beforeAll(async () => {
-  const outputDir = path.join(__dirname, './__output__')
+  const outputDir = path.join(import.meta.dirname, './__output__')
 
   for (const fixture of fixtures) {
     const name = path.basename(fixture, '.ndjson')
@@ -21,9 +21,9 @@ test.beforeAll(async () => {
       fs.createReadStream(fixture, { encoding: 'utf-8' }),
       new NdjsonToMessageStream(),
       new CucumberHtmlStream(
-        path.join(__dirname, '../dist/main.css'),
-        path.join(__dirname, '../dist/main.js'),
-        path.join(__dirname, '../dist/src/icon.url')
+        path.join(import.meta.dirname, '../dist/main.css'),
+        path.join(import.meta.dirname, '../dist/main.js'),
+        path.join(import.meta.dirname, '../dist/src/icon.url')
       ),
       fs.createWriteStream(outputFile)
     )
diff --git a/javascript/webpack.config.js b/javascript/webpack.config.js
index 5082a3eb..75861b4e 100644
--- a/javascript/webpack.config.js
+++ b/javascript/webpack.config.js
@@ -1,6 +1,6 @@
-const MiniCssExtractPlugin = require('mini-css-extract-plugin')
+import MiniCssExtractPlugin from 'mini-css-extract-plugin'
 
-module.exports = {
+export default {
   entry: './dist/src/main.js',
   module: {
     rules: [