diff --git a/.eslintrc b/.eslintrc
new file mode 100644
index 0000000..5ce8c64
--- /dev/null
+++ b/.eslintrc
@@ -0,0 +1,21 @@
+{
+  "overrides": [
+    {
+      "files": "*.ts",
+      "parser": "@typescript-eslint/parser",
+      "rules": {
+        "no-unused-vars": "off",
+        "no-useless-constructor": "off",
+        "@typescript-eslint/no-unused-vars": "error",
+        "@typescript-eslint/no-useless-constructor": "error"
+      }
+    }
+  ],
+  "parserOptions": {
+    "ecmaVersion": 2017,
+    "sourceType": "module"
+  },
+  "plugins": [
+    "@typescript-eslint/eslint-plugin"
+  ]
+}
diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 18714f3..a423c85 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -39,3 +39,25 @@ jobs:
       - run: npm install
       - run: npm test
       - run: npm run coverage
+  esm:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v1
+        with:
+          node-version: '14.x'
+      - run: npm install
+      - run: npm run test:esm
+  deno:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v1
+        with:
+          node-version: 14
+      - run: npm install
+      - run: npm run compile
+      - uses: denolib/setup-deno@v2
+      - run: |
+          deno --version
+          deno test --allow-read test/deno/y18n-test.ts
diff --git a/.github/workflows/release-please.yml b/.github/workflows/release-please.yml
index 38ace4d..2fdb821 100644
--- a/.github/workflows/release-please.yml
+++ b/.github/workflows/release-please.yml
@@ -7,8 +7,38 @@ jobs:
   release-please:
     runs-on: ubuntu-latest
     steps:
-      - uses: GoogleCloudPlatform/release-please-action@v1.6.3
+      - uses: bcoe/release-please-action@v2.0.0
+        id: release
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
           release-type: node
           package-name: y18n
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v1
+        with:
+          node-version: 14
+      - run: npm install
+      - run: npm run compile
+      - name: push Deno release
+        run: |
+          git config user.name github-actions[bot]
+          git config user.email 41898282+github-actions[bot]@users.noreply.github.com
+          git remote add gh-token "https://${{ secrets.GITHUB_TOKEN}}@github.com/yargs/y18n.git"
+          git checkout -b deno
+          git add -f build
+          git commit -a -m 'chore: ${{ steps.release.outputs.tag_name }} release'
+          git push origin +deno
+          git tag -a ${{ steps.release.outputs.tag_name }}-deno -m 'chore: ${{ steps.release.outputs.tag_name }} release'
+          git push origin ${{ steps.release.outputs.tag_name }}-deno
+        if: ${{ steps.release.outputs.release_created }}
+      - uses: actions/setup-node@v1
+        with:
+          node-version: 14
+          registry-url: 'https://external-dot-oss-automation.appspot.com/'
+        if: ${{ steps.release.outputs.release_created }}
+      - run: npm install
+        if: ${{ steps.release.outputs.release_created }}
+      - run: npm publish
+        env:
+          NODE_AUTH_TOKEN: ${{secrets.NPM_TOKEN}}
+        if: ${{ steps.release.outputs.release_created }}
diff --git a/.gitignore b/.gitignore
index 20bf8fc..6430fa7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,7 @@
 .DS_Store
 node_modules
 .nyc_output
+build
 coverage
 package-lock.json
+example.*
diff --git a/.nvmrc b/.nvmrc
deleted file mode 100644
index b009dfb..0000000
--- a/.nvmrc
+++ /dev/null
@@ -1 +0,0 @@
-lts/*
diff --git a/README.md b/README.md
index 2d0b6cc..5102bb1 100644
--- a/README.md
+++ b/README.md
@@ -48,6 +48,23 @@ output:
 
 `2 fishes foo`
 
+## Deno Example
+
+As of `v5` `y18n` supports [Deno](https://github.com/denoland/deno):
+
+```typescript
+import y18n from "https://deno.land/x/y18n/deno.ts";
+
+const __ = y18n({
+  locale: 'pirate',
+  directory: './test/locales'
+}).__
+
+console.info(__`Hi, ${'Ben'} ${'Coe'}!`)
+```
+
+You will need to run with `--allow-read` to load alternative locales.
+
 ## JSON Language Files
 
 The JSON language files should be stored in a `./locales` folder.
diff --git a/deno.ts b/deno.ts
new file mode 100644
index 0000000..b743c4f
--- /dev/null
+++ b/deno.ts
@@ -0,0 +1,9 @@
+import { y18n as _y18n } from './build/lib/index.js'
+import { Y18NOpts } from './build/lib/index.d.ts'
+import shim from './lib/platform-shims/deno.ts'
+
+const y18n = (opts: Y18NOpts) => {
+  return _y18n(opts, shim)
+}
+
+export default y18n
diff --git a/index.js b/index.js
deleted file mode 100644
index d720681..0000000
--- a/index.js
+++ /dev/null
@@ -1,188 +0,0 @@
-var fs = require('fs')
-var path = require('path')
-var util = require('util')
-
-function Y18N (opts) {
-  // configurable options.
-  opts = opts || {}
-  this.directory = opts.directory || './locales'
-  this.updateFiles = typeof opts.updateFiles === 'boolean' ? opts.updateFiles : true
-  this.locale = opts.locale || 'en'
-  this.fallbackToLanguage = typeof opts.fallbackToLanguage === 'boolean' ? opts.fallbackToLanguage : true
-
-  // internal stuff.
-  this.cache = {}
-  this.writeQueue = []
-}
-
-Y18N.prototype.__ = function () {
-  if (typeof arguments[0] !== 'string') {
-    return this._taggedLiteral.apply(this, arguments)
-  }
-  var args = Array.prototype.slice.call(arguments)
-  var str = args.shift()
-  var cb = function () {} // start with noop.
-
-  if (typeof args[args.length - 1] === 'function') cb = args.pop()
-  cb = cb || function () {} // noop.
-
-  if (!this.cache[this.locale]) this._readLocaleFile()
-
-  // we've observed a new string, update the language file.
-  if (!this.cache[this.locale][str] && this.updateFiles) {
-    this.cache[this.locale][str] = str
-
-    // include the current directory and locale,
-    // since these values could change before the
-    // write is performed.
-    this._enqueueWrite([this.directory, this.locale, cb])
-  } else {
-    cb()
-  }
-
-  return util.format.apply(util, [this.cache[this.locale][str] || str].concat(args))
-}
-
-Y18N.prototype._taggedLiteral = function (parts) {
-  var args = arguments
-  var str = ''
-  parts.forEach(function (part, i) {
-    var arg = args[i + 1]
-    str += part
-    if (typeof arg !== 'undefined') {
-      str += '%s'
-    }
-  })
-  return this.__.apply(null, [str].concat([].slice.call(arguments, 1)))
-}
-
-Y18N.prototype._enqueueWrite = function (work) {
-  this.writeQueue.push(work)
-  if (this.writeQueue.length === 1) this._processWriteQueue()
-}
-
-Y18N.prototype._processWriteQueue = function () {
-  var _this = this
-  var work = this.writeQueue[0]
-
-  // destructure the enqueued work.
-  var directory = work[0]
-  var locale = work[1]
-  var cb = work[2]
-
-  var languageFile = this._resolveLocaleFile(directory, locale)
-  var serializedLocale = JSON.stringify(this.cache[locale], null, 2)
-
-  fs.writeFile(languageFile, serializedLocale, 'utf-8', function (err) {
-    _this.writeQueue.shift()
-    if (_this.writeQueue.length > 0) _this._processWriteQueue()
-    cb(err)
-  })
-}
-
-Y18N.prototype._readLocaleFile = function () {
-  var localeLookup = {}
-  var languageFile = this._resolveLocaleFile(this.directory, this.locale)
-
-  try {
-    localeLookup = JSON.parse(fs.readFileSync(languageFile, 'utf-8'))
-  } catch (err) {
-    if (err instanceof SyntaxError) {
-      err.message = 'syntax error in ' + languageFile
-    }
-
-    if (err.code === 'ENOENT') localeLookup = {}
-    else throw err
-  }
-
-  this.cache[this.locale] = localeLookup
-}
-
-Y18N.prototype._resolveLocaleFile = function (directory, locale) {
-  var file = path.resolve(directory, './', locale + '.json')
-  if (this.fallbackToLanguage && !this._fileExistsSync(file) && ~locale.lastIndexOf('_')) {
-    // attempt fallback to language only
-    var languageFile = path.resolve(directory, './', locale.split('_')[0] + '.json')
-    if (this._fileExistsSync(languageFile)) file = languageFile
-  }
-  return file
-}
-
-// this only exists because fs.existsSync() "will be deprecated"
-// see https://nodejs.org/api/fs.html#fs_fs_existssync_path
-Y18N.prototype._fileExistsSync = function (file) {
-  try {
-    return fs.statSync(file).isFile()
-  } catch (err) {
-    return false
-  }
-}
-
-Y18N.prototype.__n = function () {
-  var args = Array.prototype.slice.call(arguments)
-  var singular = args.shift()
-  var plural = args.shift()
-  var quantity = args.shift()
-
-  var cb = function () {} // start with noop.
-  if (typeof args[args.length - 1] === 'function') cb = args.pop()
-
-  if (!this.cache[this.locale]) this._readLocaleFile()
-
-  var str = quantity === 1 ? singular : plural
-  if (this.cache[this.locale][singular]) {
-    str = this.cache[this.locale][singular][quantity === 1 ? 'one' : 'other']
-  }
-
-  // we've observed a new string, update the language file.
-  if (!this.cache[this.locale][singular] && this.updateFiles) {
-    this.cache[this.locale][singular] = {
-      one: singular,
-      other: plural
-    }
-
-    // include the current directory and locale,
-    // since these values could change before the
-    // write is performed.
-    this._enqueueWrite([this.directory, this.locale, cb])
-  } else {
-    cb()
-  }
-
-  // if a %d placeholder is provided, add quantity
-  // to the arguments expanded by util.format.
-  var values = [str]
-  if (~str.indexOf('%d')) values.push(quantity)
-
-  return util.format.apply(util, values.concat(args))
-}
-
-Y18N.prototype.setLocale = function (locale) {
-  this.locale = locale
-}
-
-Y18N.prototype.getLocale = function () {
-  return this.locale
-}
-
-Y18N.prototype.updateLocale = function (obj) {
-  if (!this.cache[this.locale]) this._readLocaleFile()
-
-  for (var key in obj) {
-    this.cache[this.locale][key] = obj[key]
-  }
-}
-
-module.exports = function (opts) {
-  var y18n = new Y18N(opts)
-
-  // bind all functions to y18n, so that
-  // they can be used in isolation.
-  for (var key in y18n) {
-    if (typeof y18n[key] === 'function') {
-      y18n[key] = y18n[key].bind(y18n)
-    }
-  }
-
-  return y18n
-}
diff --git a/index.mjs b/index.mjs
new file mode 100644
index 0000000..46c8213
--- /dev/null
+++ b/index.mjs
@@ -0,0 +1,8 @@
+import shim from './build/lib/platform-shims/node.js'
+import { y18n as _y18n } from './build/lib/index.js'
+
+const y18n = (opts) => {
+  return _y18n(opts, shim)
+}
+
+export default y18n
diff --git a/lib/cjs.ts b/lib/cjs.ts
new file mode 100644
index 0000000..1ba6a58
--- /dev/null
+++ b/lib/cjs.ts
@@ -0,0 +1,8 @@
+import { y18n as _y18n, Y18NOpts } from './index.js'
+import nodePlatformShim from './platform-shims/node.js'
+
+const y18n = (opts: Y18NOpts) => {
+  return _y18n(opts, nodePlatformShim)
+}
+
+export default y18n
diff --git a/lib/index.ts b/lib/index.ts
new file mode 100644
index 0000000..864cbac
--- /dev/null
+++ b/lib/index.ts
@@ -0,0 +1,227 @@
+export interface Y18NOpts {
+  directory?: string;
+  updateFiles?: boolean;
+  locale?: string;
+  fallbackToLanguage?: boolean;
+}
+
+interface Work {
+  directory: string;
+  locale: string;
+  cb: Function
+}
+
+export interface Locale {
+  [key: string]: string
+}
+
+interface CacheEntry {
+  [key: string]: string;
+}
+
+export interface PlatformShim {
+  fs: {
+    readFileSync: Function,
+    writeFile: Function
+  },
+  exists: Function,
+  format: Function,
+  resolve: Function
+}
+
+let shim: PlatformShim
+class Y18N {
+  directory: string;
+  updateFiles: boolean;
+  locale: string;
+  fallbackToLanguage: boolean;
+  writeQueue: Work[];
+  cache: {[key: string]: {[key: string]: CacheEntry|string}};
+
+  constructor (opts: Y18NOpts) {
+    // configurable options.
+    opts = opts || {}
+    this.directory = opts.directory || './locales'
+    this.updateFiles = typeof opts.updateFiles === 'boolean' ? opts.updateFiles : true
+    this.locale = opts.locale || 'en'
+    this.fallbackToLanguage = typeof opts.fallbackToLanguage === 'boolean' ? opts.fallbackToLanguage : true
+
+    // internal stuff.
+    this.cache = {}
+    this.writeQueue = []
+  }
+
+  __ (...args: (string|Function)[]): string {
+    if (typeof arguments[0] !== 'string') {
+      return this._taggedLiteral(arguments[0] as string[], ...arguments)
+    }
+    const str: string = args.shift() as string
+
+    let cb: Function = function () {} // start with noop.
+    if (typeof args[args.length - 1] === 'function') cb = (args.pop() as Function)
+    cb = cb || function () {} // noop.
+
+    if (!this.cache[this.locale]) this._readLocaleFile()
+
+    // we've observed a new string, update the language file.
+    if (!this.cache[this.locale][str] && this.updateFiles) {
+      this.cache[this.locale][str] = str
+
+      // include the current directory and locale,
+      // since these values could change before the
+      // write is performed.
+      this._enqueueWrite({
+        directory: this.directory,
+        locale: this.locale,
+        cb
+      })
+    } else {
+      cb()
+    }
+
+    return shim.format.apply(shim.format, [this.cache[this.locale][str] || str].concat(args as string[]))
+  }
+
+  __n () {
+    const args = Array.prototype.slice.call(arguments)
+    const singular: string = args.shift()
+    const plural: string = args.shift()
+    const quantity: number = args.shift()
+
+    let cb = function () {} // start with noop.
+    if (typeof args[args.length - 1] === 'function') cb = args.pop()
+
+    if (!this.cache[this.locale]) this._readLocaleFile()
+
+    let str = quantity === 1 ? singular : plural
+    if (this.cache[this.locale][singular]) {
+      const entry = this.cache[this.locale][singular] as CacheEntry
+      str = entry[quantity === 1 ? 'one' : 'other']
+    }
+
+    // we've observed a new string, update the language file.
+    if (!this.cache[this.locale][singular] && this.updateFiles) {
+      this.cache[this.locale][singular] = {
+        one: singular,
+        other: plural
+      }
+
+      // include the current directory and locale,
+      // since these values could change before the
+      // write is performed.
+      this._enqueueWrite({
+        directory: this.directory,
+        locale: this.locale,
+        cb
+      })
+    } else {
+      cb()
+    }
+
+    // if a %d placeholder is provided, add quantity
+    // to the arguments expanded by util.format.
+    var values: (string|number)[] = [str]
+    if (~str.indexOf('%d')) values.push(quantity)
+
+    return shim.format.apply(shim.format, values.concat(args))
+  }
+
+  setLocale (locale: string) {
+    this.locale = locale
+  }
+
+  getLocale () {
+    return this.locale
+  }
+
+  updateLocale (obj: Locale) {
+    if (!this.cache[this.locale]) this._readLocaleFile()
+
+    for (const key in obj) {
+      if (Object.prototype.hasOwnProperty.call(obj, key)) {
+        this.cache[this.locale][key] = obj[key]
+      }
+    }
+  }
+
+  _taggedLiteral (parts: string[], ...args: string[]) {
+    let str = ''
+    parts.forEach(function (part, i) {
+      var arg = args[i + 1]
+      str += part
+      if (typeof arg !== 'undefined') {
+        str += '%s'
+      }
+    })
+    return this.__.apply(this, [str].concat([].slice.call(args, 1)))
+  }
+
+  _enqueueWrite (work: Work) {
+    this.writeQueue.push(work)
+    if (this.writeQueue.length === 1) this._processWriteQueue()
+  }
+
+  _processWriteQueue () {
+    var _this = this
+    var work = this.writeQueue[0]
+
+    // destructure the enqueued work.
+    var directory = work.directory
+    var locale = work.locale
+    var cb = work.cb
+
+    var languageFile = this._resolveLocaleFile(directory, locale)
+    var serializedLocale = JSON.stringify(this.cache[locale], null, 2)
+
+    shim.fs.writeFile(languageFile, serializedLocale, 'utf-8', function (err: Error) {
+      _this.writeQueue.shift()
+      if (_this.writeQueue.length > 0) _this._processWriteQueue()
+      cb(err)
+    })
+  }
+
+  _readLocaleFile () {
+    var localeLookup = {}
+    var languageFile = this._resolveLocaleFile(this.directory, this.locale)
+
+    try {
+      localeLookup = JSON.parse(shim.fs.readFileSync(languageFile, 'utf-8'))
+    } catch (err) {
+      if (err instanceof SyntaxError) {
+        err.message = 'syntax error in ' + languageFile
+      }
+
+      if (err.code === 'ENOENT') localeLookup = {}
+      else throw err
+    }
+
+    this.cache[this.locale] = localeLookup
+  }
+
+  _resolveLocaleFile (directory: string, locale: string) {
+    var file = shim.resolve(directory, './', locale + '.json')
+    if (this.fallbackToLanguage && !this._fileExistsSync(file) && ~locale.lastIndexOf('_')) {
+      // attempt fallback to language only
+      var languageFile = shim.resolve(directory, './', locale.split('_')[0] + '.json')
+      if (this._fileExistsSync(languageFile)) file = languageFile
+    }
+    return file
+  }
+
+  _fileExistsSync (file: string) {
+    return shim.exists(file)
+  }
+}
+
+export function y18n (opts: Y18NOpts, _shim: PlatformShim) {
+  shim = _shim
+  const y18n = new Y18N(opts)
+  return {
+    __: y18n.__.bind(y18n),
+    __n: y18n.__n.bind(y18n),
+    setLocale: y18n.setLocale.bind(y18n),
+    getLocale: y18n.getLocale.bind(y18n),
+    updateLocale: y18n.updateLocale.bind(y18n),
+    locale: y18n.locale
+  }
+}
diff --git a/lib/platform-shims/deno.ts b/lib/platform-shims/deno.ts
new file mode 100644
index 0000000..3cd243e
--- /dev/null
+++ b/lib/platform-shims/deno.ts
@@ -0,0 +1,34 @@
+/* global Deno */
+
+import { posix } from 'https://deno.land/std/path/mod.ts'
+import { sprintf } from 'https://deno.land/std/fmt/printf.ts'
+
+export default {
+  fs: {
+    readFileSync: (path: string) => {
+      try {
+        return Deno.readTextFileSync(path)
+      } catch (err) {
+        // Fake the same error as Node.js, so that it does not bubble.
+        err.code = 'ENOENT'
+        throw err
+      }
+    },
+    writeFile: Deno.writeFile
+  },
+  format: sprintf,
+  resolve: (base: string, p1: string, p2: string) => {
+    try {
+      return posix.resolve(base, p1, p2)
+    } catch (err) {
+      // Most likely we simply don't have --allow-read set.
+    }
+  },
+  exists: (file: string) => {
+    try {
+      return Deno.statSync(file).isFile
+    } catch (err) {
+      return false
+    }
+  }
+}
diff --git a/lib/platform-shims/node.ts b/lib/platform-shims/node.ts
new file mode 100644
index 0000000..2d40e7b
--- /dev/null
+++ b/lib/platform-shims/node.ts
@@ -0,0 +1,19 @@
+import { readFileSync, statSync, writeFile } from 'fs'
+import { format } from 'util'
+import { resolve } from 'path'
+
+export default {
+  fs: {
+    readFileSync,
+    writeFile
+  },
+  format,
+  resolve,
+  exists: (file: string) => {
+    try {
+      return statSync(file).isFile()
+    } catch (err) {
+      return false
+    }
+  }
+}
diff --git a/package.json b/package.json
index ad989b6..df42208 100644
--- a/package.json
+++ b/package.json
@@ -2,6 +2,13 @@
   "name": "y18n",
   "version": "4.0.0",
   "description": "the bare-bones internationalization library used by yargs",
+  "exports": {
+    "import": "./index.mjs",
+    "require": "./build/index.cjs"
+  },
+  "type": "module",
+  "module": "./build/lib/index.js",
+  "types": "./build/index.cjs.d.ts",
   "keywords": [
     "i18n",
     "internationalization",
@@ -18,23 +25,45 @@
   "license": "ISC",
   "author": "Ben Coe <bencoe@gmail.com>",
   "main": "index.js",
-  "files": [
-    "index.js"
-  ],
   "scripts": {
-    "fix": "standard --fix",
-    "coverage": "c8 --check-coverage report",
-    "pretest": "standard",
-    "test": "c8 mocha"
+    "check": "standardx '**/*.ts' '**/*.cjs' '**/*.mjs'",
+    "fix": "standardx --fix '**/*.ts' '**/*.cjs' '**/*.mjs'",
+    "pretest": "rimraf build && tsc -p tsconfig.test.json && cross-env NODE_ENV=test npm run build:cjs",
+    "test": "c8 --reporter=text --reporter=html mocha test/*.cjs",
+    "test:esm": "c8 --reporter=text --reporter=html mocha test/esm/*.mjs",
+    "posttest": "npm run check",
+    "coverage": "c8 report --check-coverage",
+    "precompile": "rimraf build",
+    "compile": "tsc",
+    "postcompile": "npm run build:cjs",
+    "build:cjs": "rollup -c",
+    "prepare": "npm run compile"
   },
   "devDependencies": {
+    "@types/node": "^14.6.4",
+    "@wessberg/rollup-plugin-ts": "^1.3.1",
     "c8": "^7.3.0",
     "chai": "^4.0.1",
+    "cross-env": "^7.0.2",
+    "gts": "^2.0.2",
     "mocha": "^8.0.0",
     "rimraf": "^3.0.2",
-    "standard": "^14.3.4"
+    "rollup": "^2.26.10",
+    "standardx": "^5.0.0",
+    "ts-transform-default-export": "^1.0.2",
+    "typescript": "^3.9.7"
   },
+  "files": [
+    "build",
+    "index.mjs",
+    "!*.d.ts"
+  ],
   "engines": {
     "node": ">=10"
+  },
+  "standardx": {
+    "ignore": [
+      "build"
+    ]
   }
 }
diff --git a/rollup.config.js b/rollup.config.js
new file mode 100644
index 0000000..537ce1e
--- /dev/null
+++ b/rollup.config.js
@@ -0,0 +1,22 @@
+import ts from '@wessberg/rollup-plugin-ts'
+import transformDefaultExport from 'ts-transform-default-export'
+
+const output = {
+  format: 'cjs',
+  file: './build/index.cjs',
+  exports: 'default'
+}
+
+if (process.env.NODE_ENV === 'test') output.sourcemap = true
+
+export default {
+  input: './lib/cjs.ts',
+  output,
+  plugins: [
+    ts({
+      transformers: ({ program }) => ({
+        afterDeclarations: transformDefaultExport(program)
+      })
+    }),
+  ]
+}
diff --git a/test/deno/y18n-test.ts b/test/deno/y18n-test.ts
new file mode 100644
index 0000000..9b1b497
--- /dev/null
+++ b/test/deno/y18n-test.ts
@@ -0,0 +1,19 @@
+/* global Deno */
+
+import {
+  assertEquals
+} from 'https://deno.land/std/testing/asserts.ts'
+import y18n from '../../deno.ts'
+
+// Parser:
+Deno.test('smoke test', () => {
+  const __ = y18n({
+    locale: 'pirate',
+    directory: './test/locales'
+  }).__
+
+  assertEquals(
+    __`Hi, ${'Ben'} ${'Coe'}!`,
+    'Yarr! Shiver me timbers, why \'tis Ben Coe!'
+  )
+})
diff --git a/test/esm/y18n-test.mjs b/test/esm/y18n-test.mjs
new file mode 100644
index 0000000..c8675ae
--- /dev/null
+++ b/test/esm/y18n-test.mjs
@@ -0,0 +1,18 @@
+/* global describe, it */
+
+import * as assert from 'assert'
+import y18n from '../../index.mjs'
+
+describe('y18n', function () {
+  it('__ smoke test', function () {
+    const __ = y18n({
+      locale: 'pirate',
+      directory: './test/locales'
+    }).__
+
+    assert.strictEqual(
+      __`Hi, ${'Ben'} ${'Coe'}!`,
+      'Yarr! Shiver me timbers, why \'tis Ben Coe!'
+    )
+  })
+})
diff --git a/test/y18n-test.js b/test/y18n-test.cjs
similarity index 98%
rename from test/y18n-test.js
rename to test/y18n-test.cjs
index e96e8e6..d65b14b 100644
--- a/test/y18n-test.js
+++ b/test/y18n-test.cjs
@@ -1,17 +1,17 @@
 /* global describe, it, after, beforeEach */
 
-var expect = require('chai').expect
-var fs = require('fs')
-var rimraf = require('rimraf')
-var y18n = require('../')
-var path = require('path')
+const expect = require('chai').expect
+const fs = require('fs')
+const rimraf = require('rimraf')
+const y18n = require('../build/index.cjs')
+const path = require('path')
 
 require('chai').should()
 
 describe('y18n', function () {
   describe('configure', function () {
     it('allows you to override the default y18n configuration', function () {
-      var y = y18n({ locale: 'fr' })
+      const y = y18n({ locale: 'fr' })
       y.locale.should.equal('fr')
     })
   })
@@ -43,7 +43,6 @@ describe('y18n', function () {
         locale: 'pirate',
         directory: path.join(__dirname, 'locales')
       }).__
-
       __`Hi, ${'Ben'} ${''}!`.should.equal('Yarr! Shiver me timbers, why \'tis Ben !')
     })
     it('uses replacements from the default locale if none is configured', function () {
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..9318745
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,17 @@
+{
+  "extends": "./node_modules/gts/tsconfig-google.json",
+  "compilerOptions": {
+    "outDir": "build",
+    "rootDir": ".",
+    "sourceMap": false,
+    "target": "es2017",
+    "moduleResolution": "node",
+    "module": "es2015"
+  },  
+  "include": [
+    "lib/**/*.ts"
+  ],
+  "exclude": [
+    "lib/platform-shims/deno.ts"
+  ]
+}
\ No newline at end of file
diff --git a/tsconfig.test.json b/tsconfig.test.json
new file mode 100644
index 0000000..b2175ed
--- /dev/null
+++ b/tsconfig.test.json
@@ -0,0 +1,9 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "sourceMap": true
+  },
+  "exclude": [
+    "lib/platform-shims/deno.ts"
+  ]
+}