diff --git a/.eslintrc.yml b/.eslintrc.yml
index 0733e51..080b4b7 100644
--- a/.eslintrc.yml
+++ b/.eslintrc.yml
@@ -5,10 +5,10 @@ env:
 plugins:
   - jest
 ignorePatterns:
-  - "**/*.test.js"
+  - "**/*.d.ts"
 extends:
   - eslint:recommended
   - prettier
 parserOptions:
-  ecmaVersion: 2021
+  ecmaVersion: 2022
   sourceType: module
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 456dfaf..99e91d3 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -4,8 +4,10 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install modules
         run: yarn
       - name: Run lint
         run: yarn lint
+      - name: Run lint
+        run: yarn test
diff --git a/.gitignore b/.gitignore
index 682446c..3ca6a9c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,7 +1,6 @@
 # Don't edit this part
 
 .yarn/cache/*.zip
-coverage_cjs
 
 # Created by https://www.toptal.com/developers/gitignore/api/node,intellij+all,yarn
 # Edit at https://www.toptal.com/developers/gitignore?templates=node,intellij+all,yarn
diff --git a/.husky/pre-commit b/.husky/pre-commit
index e136717..8a31f84 100755
--- a/.husky/pre-commit
+++ b/.husky/pre-commit
@@ -3,4 +3,4 @@
 
 yarn lint
 yarn test
-git add index.esm.js index.cjs index.esm.d.ts
+git add index.js index.d.ts
diff --git a/.nvmrc b/.nvmrc
index d939939..02c8b48 100644
--- a/.nvmrc
+++ b/.nvmrc
@@ -1 +1 @@
-18.13.0
+18.18.0
diff --git a/README.md b/README.md
index 539f1e9..be04dc5 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,106 @@
+[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
+![Static Badge](https://img.shields.io/badge/coverage-100-brightgreen)
+![Static Badge](https://img.shields.io/badge/release-3.0.1-blue)
+[![test](https://github.com/mathrobin/lambda-returns/actions/workflows/test.yml/badge.svg)](https://github.com/mathrobin/lambda-returns/actions/workflows/test.yml)
+
 # lambda-returns
+
+Provides shorthand to manage AWS lambda result. And provides test helper methods too!
+
+ESM only since v3. Typings included.
+
+## Usage
+
+Deadly simple
+
+```javascript
+import { ok, internalServerError } from "lambda-returns";
+
+export default async () => {
+  try {
+
+    return ok({
+      status: "success"
+    });
+  } catch (err) {
+
+    return internalServerError({
+      status: "error",
+      error: err
+    });
+  }
+}
+```
+
+instead of that non-funny code:
+
+```javascript
+export default async () => {
+  try {
+
+    return {
+      statusCode: 200,
+      body: JSON.stringify({
+        status: "success"
+      }),
+    };
+  } catch (err) {
+
+    return {
+      statusCode: 500,
+      body: JSON.stringify({
+        status: "error",
+        error: err
+      }),
+    };
+  }
+}
+```
+
+### Test helpers methods
+
+Not enough for you? For me too. This package provides a simple way to test your return result from your AWS lambda
+handler method.
+
+```javascript
+import { isOk, isBadRequest } from "lambda-returns";
+
+expect(isOk(result)).toBeTruthy();
+expect(isBadRequest(result)).toBeTruthy();
+```
+
+## Pros
+
+- No prod dependency
+- Typings provided
+- lower than 45kB unpacked
+
+### Stop remember codes
+
+You don't have to remember status code values. Just the name which is more "menaningful". Who really knows the code of:
+
+- insufficientStorage
+- partialContent
+- imATeapot
+  . You ? Me no. And don't want/need to.
+
+### Stop polluting your business logic
+
+Moreover, into vanilla AWS lambda way, you need to return a string as body. But just stringify your result is dangerous,
+if you have a dynamic result, maybe is null, maybe is undefined, maybe you already have a string.
+
+F*ck! I don't want to care of it in my business logic! `lambda-returns` manages it for you.
+
+## Cons
+
+There is only one known pitfall. We can't technically export "continue" status due to it's a reserved word in
+JavaScript.
+
+```javascript
+export const continue
+= {}; // or whatever;
+```
+
+This is just forbidden. If you knwon any way to go over this problem, tell me.
+
+Despite to this problem, test helper method `isContinue` is available. 
diff --git a/build.js b/build.js
index 2969e8d..d5445fa 100644
--- a/build.js
+++ b/build.js
@@ -1,70 +1,9 @@
 import fs from 'fs';
 
-const codes = {
-  continue: 100,
-  switchingProtocols: 101,
-  processing: 102,
-  ok: 200,
-  created: 201,
-  accepted: 202,
-  nonAuthoritativeInformation: 203,
-  noContent: 204,
-  resetContent: 205,
-  partialContent: 206,
-  multiStatus: 207,
-  multipleChoices: 300,
-  movedPermanently: 301,
-  movedTemporarily: 302,
-  seeOther: 303,
-  notModified: 304,
-  useProxy: 305,
-  temporaryRedirect: 307,
-  badRequest: 400,
-  unauthorized: 401,
-  paymentRequired: 402,
-  forbidden: 403,
-  notFound: 404,
-  methodNotAllowed: 405,
-  notAcceptable: 406,
-  proxyAuthenticationRequired: 407,
-  requestTimeOut: 408,
-  conflict: 409,
-  gone: 410,
-  lengthRequired: 411,
-  preconditionFailed: 412,
-  requestEntityTooLarge: 413,
-  requestUriTooLarge: 414,
-  unsupportedMediaType: 415,
-  requestedRangeNotSatisfiable: 416,
-  expectationFailed: 417,
-  imATeapot: 418,
-  unprocessableEntity: 422,
-  locked: 423,
-  failedDependency: 424,
-  unorderedCollection: 425,
-  upgradeRequired: 426,
-  preconditionRequired: 428,
-  tooManyRequests: 429,
-  requestHeaderFieldsTooLarge: 431,
-  internalServerError: 500,
-  notImplemented: 501,
-  badGateway: 502,
-  serviceUnavailable: 503,
-  gatewayTimeOut: 504,
-  httpVersionNotSupported: 505,
-  variantAlsoNegotiates: 506,
-  insufficientStorage: 507,
-  bandwidthLimitExceeded: 509,
-  notExtended: 510,
-  networkAuthenticationRequired: 511,
-};
+import capitalizeFirstLetter from './src/capitalize_first/index.js';
+import codes from './codes.js';
 
 const exportsEsm = [];
-const exportsCjs = [];
-
-function capitalizeFirstLetter(string) {
-  return string[0].toUpperCase() + string.slice(1);
-}
 
 Object.entries(codes)
   .filter(([message]) => {
@@ -77,12 +16,6 @@ Object.entries(codes)
     headers,
     body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
 });`);
-
-    exportsCjs.push(`module.exports.${message} = (result, headers = {}) => ({
-    statusCode: ${code},
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});`);
   });
 
 Object.entries(codes).forEach(([message, code]) => {
@@ -91,17 +24,8 @@ Object.entries(codes).forEach(([message, code]) => {
   )} = (response) => {
     return response.statusCode === ${code};
 };`);
-
-  exportsCjs.push(`module.exports.is${capitalizeFirstLetter(
-    message
-  )} = (response) => {
-    return response.statusCode === ${code};
-};`);
 });
 
-fs.writeFile('./index.esm.js', exportsEsm.join('\n\n'), () => {
-  console.log('Version ES Module generated');
-});
-fs.writeFile('./index.cjs', exportsCjs.join('\n\n'), () => {
-  console.log('Version CommonJs generated');
+fs.writeFile('./index.js', exportsEsm.join('\n\n'), () => {
+  console.log('Module generated');
 });
diff --git a/codes.js b/codes.js
new file mode 100644
index 0000000..2dc4509
--- /dev/null
+++ b/codes.js
@@ -0,0 +1,58 @@
+export default {
+  continue: 100,
+  switchingProtocols: 101,
+  processing: 102,
+  ok: 200,
+  created: 201,
+  accepted: 202,
+  nonAuthoritativeInformation: 203,
+  noContent: 204,
+  resetContent: 205,
+  partialContent: 206,
+  multiStatus: 207,
+  multipleChoices: 300,
+  movedPermanently: 301,
+  movedTemporarily: 302,
+  seeOther: 303,
+  notModified: 304,
+  useProxy: 305,
+  temporaryRedirect: 307,
+  badRequest: 400,
+  unauthorized: 401,
+  paymentRequired: 402,
+  forbidden: 403,
+  notFound: 404,
+  methodNotAllowed: 405,
+  notAcceptable: 406,
+  proxyAuthenticationRequired: 407,
+  requestTimeOut: 408,
+  conflict: 409,
+  gone: 410,
+  lengthRequired: 411,
+  preconditionFailed: 412,
+  requestEntityTooLarge: 413,
+  requestUriTooLarge: 414,
+  unsupportedMediaType: 415,
+  requestedRangeNotSatisfiable: 416,
+  expectationFailed: 417,
+  imATeapot: 418,
+  unprocessableEntity: 422,
+  locked: 423,
+  failedDependency: 424,
+  unorderedCollection: 425,
+  upgradeRequired: 426,
+  preconditionRequired: 428,
+  tooManyRequests: 429,
+  requestHeaderFieldsTooLarge: 431,
+  internalServerError: 500,
+  notImplemented: 501,
+  badGateway: 502,
+  serviceUnavailable: 503,
+  gatewayTimeOut: 504,
+  httpVersionNotSupported: 505,
+  variantAlsoNegotiates: 506,
+  insufficientStorage: 507,
+  bandwidthLimitExceeded: 509,
+  notExtended: 510,
+  networkAuthenticationRequired: 511,
+};
diff --git a/index.cjs b/index.cjs
deleted file mode 100644
index 7ddb698..0000000
--- a/index.cjs
+++ /dev/null
@@ -1,553 +0,0 @@
-module.exports.switchingProtocols = (result, headers = {}) => ({
-    statusCode: 101,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.processing = (result, headers = {}) => ({
-    statusCode: 102,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.ok = (result, headers = {}) => ({
-    statusCode: 200,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.created = (result, headers = {}) => ({
-    statusCode: 201,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.accepted = (result, headers = {}) => ({
-    statusCode: 202,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.nonAuthoritativeInformation = (result, headers = {}) => ({
-    statusCode: 203,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.noContent = (result, headers = {}) => ({
-    statusCode: 204,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.resetContent = (result, headers = {}) => ({
-    statusCode: 205,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.partialContent = (result, headers = {}) => ({
-    statusCode: 206,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.multiStatus = (result, headers = {}) => ({
-    statusCode: 207,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.multipleChoices = (result, headers = {}) => ({
-    statusCode: 300,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.movedPermanently = (result, headers = {}) => ({
-    statusCode: 301,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.movedTemporarily = (result, headers = {}) => ({
-    statusCode: 302,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.seeOther = (result, headers = {}) => ({
-    statusCode: 303,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.notModified = (result, headers = {}) => ({
-    statusCode: 304,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.useProxy = (result, headers = {}) => ({
-    statusCode: 305,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.temporaryRedirect = (result, headers = {}) => ({
-    statusCode: 307,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.badRequest = (result, headers = {}) => ({
-    statusCode: 400,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.unauthorized = (result, headers = {}) => ({
-    statusCode: 401,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.paymentRequired = (result, headers = {}) => ({
-    statusCode: 402,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.forbidden = (result, headers = {}) => ({
-    statusCode: 403,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.notFound = (result, headers = {}) => ({
-    statusCode: 404,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.methodNotAllowed = (result, headers = {}) => ({
-    statusCode: 405,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.notAcceptable = (result, headers = {}) => ({
-    statusCode: 406,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.proxyAuthenticationRequired = (result, headers = {}) => ({
-    statusCode: 407,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.requestTimeOut = (result, headers = {}) => ({
-    statusCode: 408,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.conflict = (result, headers = {}) => ({
-    statusCode: 409,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.gone = (result, headers = {}) => ({
-    statusCode: 410,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.lengthRequired = (result, headers = {}) => ({
-    statusCode: 411,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.preconditionFailed = (result, headers = {}) => ({
-    statusCode: 412,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.requestEntityTooLarge = (result, headers = {}) => ({
-    statusCode: 413,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.requestUriTooLarge = (result, headers = {}) => ({
-    statusCode: 414,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.unsupportedMediaType = (result, headers = {}) => ({
-    statusCode: 415,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.requestedRangeNotSatisfiable = (result, headers = {}) => ({
-    statusCode: 416,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.expectationFailed = (result, headers = {}) => ({
-    statusCode: 417,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.imATeapot = (result, headers = {}) => ({
-    statusCode: 418,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.unprocessableEntity = (result, headers = {}) => ({
-    statusCode: 422,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.locked = (result, headers = {}) => ({
-    statusCode: 423,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.failedDependency = (result, headers = {}) => ({
-    statusCode: 424,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.unorderedCollection = (result, headers = {}) => ({
-    statusCode: 425,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.upgradeRequired = (result, headers = {}) => ({
-    statusCode: 426,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.preconditionRequired = (result, headers = {}) => ({
-    statusCode: 428,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.tooManyRequests = (result, headers = {}) => ({
-    statusCode: 429,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.requestHeaderFieldsTooLarge = (result, headers = {}) => ({
-    statusCode: 431,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.internalServerError = (result, headers = {}) => ({
-    statusCode: 500,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.notImplemented = (result, headers = {}) => ({
-    statusCode: 501,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.badGateway = (result, headers = {}) => ({
-    statusCode: 502,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.serviceUnavailable = (result, headers = {}) => ({
-    statusCode: 503,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.gatewayTimeOut = (result, headers = {}) => ({
-    statusCode: 504,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.httpVersionNotSupported = (result, headers = {}) => ({
-    statusCode: 505,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.variantAlsoNegotiates = (result, headers = {}) => ({
-    statusCode: 506,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.insufficientStorage = (result, headers = {}) => ({
-    statusCode: 507,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.bandwidthLimitExceeded = (result, headers = {}) => ({
-    statusCode: 509,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.notExtended = (result, headers = {}) => ({
-    statusCode: 510,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.networkAuthenticationRequired = (result, headers = {}) => ({
-    statusCode: 511,
-    headers,
-    body: result ? typeof result === 'string' ? result : JSON.stringify(result) : null,
-});
-
-module.exports.isContinue = (response) => {
-    return response.statusCode === 100;
-};
-
-module.exports.isSwitchingProtocols = (response) => {
-    return response.statusCode === 101;
-};
-
-module.exports.isProcessing = (response) => {
-    return response.statusCode === 102;
-};
-
-module.exports.isOk = (response) => {
-    return response.statusCode === 200;
-};
-
-module.exports.isCreated = (response) => {
-    return response.statusCode === 201;
-};
-
-module.exports.isAccepted = (response) => {
-    return response.statusCode === 202;
-};
-
-module.exports.isNonAuthoritativeInformation = (response) => {
-    return response.statusCode === 203;
-};
-
-module.exports.isNoContent = (response) => {
-    return response.statusCode === 204;
-};
-
-module.exports.isResetContent = (response) => {
-    return response.statusCode === 205;
-};
-
-module.exports.isPartialContent = (response) => {
-    return response.statusCode === 206;
-};
-
-module.exports.isMultiStatus = (response) => {
-    return response.statusCode === 207;
-};
-
-module.exports.isMultipleChoices = (response) => {
-    return response.statusCode === 300;
-};
-
-module.exports.isMovedPermanently = (response) => {
-    return response.statusCode === 301;
-};
-
-module.exports.isMovedTemporarily = (response) => {
-    return response.statusCode === 302;
-};
-
-module.exports.isSeeOther = (response) => {
-    return response.statusCode === 303;
-};
-
-module.exports.isNotModified = (response) => {
-    return response.statusCode === 304;
-};
-
-module.exports.isUseProxy = (response) => {
-    return response.statusCode === 305;
-};
-
-module.exports.isTemporaryRedirect = (response) => {
-    return response.statusCode === 307;
-};
-
-module.exports.isBadRequest = (response) => {
-    return response.statusCode === 400;
-};
-
-module.exports.isUnauthorized = (response) => {
-    return response.statusCode === 401;
-};
-
-module.exports.isPaymentRequired = (response) => {
-    return response.statusCode === 402;
-};
-
-module.exports.isForbidden = (response) => {
-    return response.statusCode === 403;
-};
-
-module.exports.isNotFound = (response) => {
-    return response.statusCode === 404;
-};
-
-module.exports.isMethodNotAllowed = (response) => {
-    return response.statusCode === 405;
-};
-
-module.exports.isNotAcceptable = (response) => {
-    return response.statusCode === 406;
-};
-
-module.exports.isProxyAuthenticationRequired = (response) => {
-    return response.statusCode === 407;
-};
-
-module.exports.isRequestTimeOut = (response) => {
-    return response.statusCode === 408;
-};
-
-module.exports.isConflict = (response) => {
-    return response.statusCode === 409;
-};
-
-module.exports.isGone = (response) => {
-    return response.statusCode === 410;
-};
-
-module.exports.isLengthRequired = (response) => {
-    return response.statusCode === 411;
-};
-
-module.exports.isPreconditionFailed = (response) => {
-    return response.statusCode === 412;
-};
-
-module.exports.isRequestEntityTooLarge = (response) => {
-    return response.statusCode === 413;
-};
-
-module.exports.isRequestUriTooLarge = (response) => {
-    return response.statusCode === 414;
-};
-
-module.exports.isUnsupportedMediaType = (response) => {
-    return response.statusCode === 415;
-};
-
-module.exports.isRequestedRangeNotSatisfiable = (response) => {
-    return response.statusCode === 416;
-};
-
-module.exports.isExpectationFailed = (response) => {
-    return response.statusCode === 417;
-};
-
-module.exports.isImATeapot = (response) => {
-    return response.statusCode === 418;
-};
-
-module.exports.isUnprocessableEntity = (response) => {
-    return response.statusCode === 422;
-};
-
-module.exports.isLocked = (response) => {
-    return response.statusCode === 423;
-};
-
-module.exports.isFailedDependency = (response) => {
-    return response.statusCode === 424;
-};
-
-module.exports.isUnorderedCollection = (response) => {
-    return response.statusCode === 425;
-};
-
-module.exports.isUpgradeRequired = (response) => {
-    return response.statusCode === 426;
-};
-
-module.exports.isPreconditionRequired = (response) => {
-    return response.statusCode === 428;
-};
-
-module.exports.isTooManyRequests = (response) => {
-    return response.statusCode === 429;
-};
-
-module.exports.isRequestHeaderFieldsTooLarge = (response) => {
-    return response.statusCode === 431;
-};
-
-module.exports.isInternalServerError = (response) => {
-    return response.statusCode === 500;
-};
-
-module.exports.isNotImplemented = (response) => {
-    return response.statusCode === 501;
-};
-
-module.exports.isBadGateway = (response) => {
-    return response.statusCode === 502;
-};
-
-module.exports.isServiceUnavailable = (response) => {
-    return response.statusCode === 503;
-};
-
-module.exports.isGatewayTimeOut = (response) => {
-    return response.statusCode === 504;
-};
-
-module.exports.isHttpVersionNotSupported = (response) => {
-    return response.statusCode === 505;
-};
-
-module.exports.isVariantAlsoNegotiates = (response) => {
-    return response.statusCode === 506;
-};
-
-module.exports.isInsufficientStorage = (response) => {
-    return response.statusCode === 507;
-};
-
-module.exports.isBandwidthLimitExceeded = (response) => {
-    return response.statusCode === 509;
-};
-
-module.exports.isNotExtended = (response) => {
-    return response.statusCode === 510;
-};
-
-module.exports.isNetworkAuthenticationRequired = (response) => {
-    return response.statusCode === 511;
-};
\ No newline at end of file
diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..de6b633
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1,441 @@
+export function switchingProtocols<T>(result: unknown, headers?: T): {
+    statusCode: 101;
+    headers: T | {};
+    body: string;
+};
+
+export function processing<T>(result: unknown, headers?: T): {
+    statusCode: 102;
+    headers: T | {};
+    body: string;
+};
+
+export function ok<T>(result: unknown, headers?: T): {
+    statusCode: 200;
+    headers: T | {};
+    body: string;
+};
+
+export function created<T>(result: unknown, headers?: T): {
+    statusCode: 201;
+    headers: T | {};
+    body: string;
+};
+
+export function accepted<T>(result: unknown, headers?: T): {
+    statusCode: 202;
+    headers: T | {};
+    body: string;
+};
+
+export function nonAuthoritativeInformation<T>(result: unknown, headers?: T): {
+    statusCode: 203;
+    headers: T | {};
+    body: string;
+};
+
+export function noContent<T>(result: unknown, headers?: T): {
+    statusCode: 204;
+    headers: T | {};
+    body: string;
+};
+
+export function resetContent<T>(result: unknown, headers?: T): {
+    statusCode: 205;
+    headers: T | {};
+    body: string;
+};
+
+export function partialContent<T>(result: unknown, headers?: T): {
+    statusCode: 206;
+    headers: T | {};
+    body: string;
+};
+
+export function multiStatus<T>(result: unknown, headers?: T): {
+    statusCode: 207;
+    headers: T | {};
+    body: string;
+};
+
+export function multipleChoices<T>(result: unknown, headers?: T): {
+    statusCode: 300;
+    headers: T | {};
+    body: string;
+};
+
+export function movedPermanently<T>(result: unknown, headers?: T): {
+    statusCode: 301;
+    headers: T | {};
+    body: string;
+};
+
+export function movedTemporarily<T>(result: unknown, headers?: T): {
+    statusCode: 302;
+    headers: T | {};
+    body: string;
+};
+
+export function seeOther<T>(result: unknown, headers?: T): {
+    statusCode: 303;
+    headers: T | {};
+    body: string;
+};
+
+export function notModified<T>(result: unknown, headers?: T): {
+    statusCode: 304;
+    headers: T | {};
+    body: string;
+};
+
+export function useProxy<T>(result: unknown, headers?: T): {
+    statusCode: 305;
+    headers: T | {};
+    body: string;
+};
+
+export function temporaryRedirect<T>(result: unknown, headers?: T): {
+    statusCode: 307;
+    headers: T | {};
+    body: string;
+};
+
+export function badRequest<T>(result: unknown, headers?: T): {
+    statusCode: 400;
+    headers: T | {};
+    body: string;
+};
+
+export function unauthorized<T>(result: unknown, headers?: T): {
+    statusCode: 401;
+    headers: T | {};
+    body: string;
+};
+
+export function paymentRequired<T>(result: unknown, headers?: T): {
+    statusCode: 402;
+    headers: T | {};
+    body: string;
+};
+
+export function forbidden<T>(result: unknown, headers?: T): {
+    statusCode: 403;
+    headers: T | {};
+    body: string;
+};
+
+export function notFound<T>(result: unknown, headers?: T): {
+    statusCode: 404;
+    headers: T | {};
+    body: string;
+};
+
+export function methodNotAllowed<T>(result: unknown, headers?: T): {
+    statusCode: 405;
+    headers: T | {};
+    body: string;
+};
+
+export function notAcceptable<T>(result: unknown, headers?: T): {
+    statusCode: 406;
+    headers: T | {};
+    body: string;
+};
+
+export function proxyAuthenticationRequired<T>(result: unknown, headers?: T): {
+    statusCode: 407;
+    headers: T | {};
+    body: string;
+};
+
+export function requestTimeOut<T>(result: unknown, headers?: T): {
+    statusCode: 408;
+    headers: T | {};
+    body: string;
+};
+
+export function conflict<T>(result: unknown, headers?: T): {
+    statusCode: 409;
+    headers: T | {};
+    body: string;
+};
+
+export function gone<T>(result: unknown, headers?: T): {
+    statusCode: 410;
+    headers: T | {};
+    body: string;
+};
+
+export function lengthRequired<T>(result: unknown, headers?: T): {
+    statusCode: 411;
+    headers: T | {};
+    body: string;
+};
+
+export function preconditionFailed<T>(result: unknown, headers?: T): {
+    statusCode: 412;
+    headers: T | {};
+    body: string;
+};
+
+export function requestEntityTooLarge<T>(result: unknown, headers?: T): {
+    statusCode: 413;
+    headers: T | {};
+    body: string;
+};
+
+export function requestUriTooLarge<T>(result: unknown, headers?: T): {
+    statusCode: 414;
+    headers: T | {};
+    body: string;
+};
+
+export function unsupportedMediaType<T>(result: unknown, headers?: T): {
+    statusCode: 415;
+    headers: T | {};
+    body: string;
+};
+
+export function requestedRangeNotSatisfiable<T>(result: unknown, headers?: T): {
+    statusCode: 416;
+    headers: T | {};
+    body: string;
+};
+
+export function expectationFailed<T>(result: unknown, headers?: T): {
+    statusCode: 417;
+    headers: T | {};
+    body: string;
+};
+
+export function imATeapot<T>(result: unknown, headers?: T): {
+    statusCode: 418;
+    headers: T | {};
+    body: string;
+};
+
+export function unprocessableEntity<T>(result: unknown, headers?: T): {
+    statusCode: 422;
+    headers: T | {};
+    body: string;
+};
+
+export function locked<T>(result: unknown, headers?: T): {
+    statusCode: 423;
+    headers: T | {};
+    body: string;
+};
+
+export function failedDependency<T>(result: unknown, headers?: T): {
+    statusCode: 424;
+    headers: T | {};
+    body: string;
+};
+
+export function unorderedCollection<T>(result: unknown, headers?: T): {
+    statusCode: 425;
+    headers: T | {};
+    body: string;
+};
+
+export function upgradeRequired<T>(result: unknown, headers?: T): {
+    statusCode: 426;
+    headers: T | {};
+    body: string;
+};
+
+export function preconditionRequired<T>(result: unknown, headers?: T): {
+    statusCode: 428;
+    headers: T | {};
+    body: string;
+};
+
+export function tooManyRequests<T>(result: unknown, headers?: T): {
+    statusCode: 429;
+    headers: T | {};
+    body: string;
+};
+
+export function requestHeaderFieldsTooLarge<T>(result: unknown, headers?: T): {
+    statusCode: 431;
+    headers: T | {};
+    body: string;
+};
+
+export function internalServerError<T>(result: unknown, headers?: T): {
+    statusCode: 500;
+    headers: T | {};
+    body: string;
+};
+
+export function notImplemented<T>(result: unknown, headers?: T): {
+    statusCode: 501;
+    headers: T | {};
+    body: string;
+};
+
+export function badGateway<T>(result: unknown, headers?: T): {
+    statusCode: 502;
+    headers: T | {};
+    body: string;
+};
+
+export function serviceUnavailable<T>(result: unknown, headers?: T): {
+    statusCode: 503;
+    headers: T | {};
+    body: string;
+};
+
+export function gatewayTimeOut<T>(result: unknown, headers?: T): {
+    statusCode: 504;
+    headers: T | {};
+    body: string;
+};
+
+export function httpVersionNotSupported<T>(result: unknown, headers?: T): {
+    statusCode: 505;
+    headers: T | {};
+    body: string;
+};
+
+export function variantAlsoNegotiates<T>(result: unknown, headers?: T): {
+    statusCode: 506;
+    headers: T | {};
+    body: string;
+};
+
+export function insufficientStorage<T>(result: unknown, headers?: T): {
+    statusCode: 507;
+    headers: T | {};
+    body: string;
+};
+
+export function bandwidthLimitExceeded<T>(result: unknown, headers?: T): {
+    statusCode: 509;
+    headers: T | {};
+    body: string;
+};
+
+export function notExtended<T>(result: unknown, headers?: T): {
+    statusCode: 510;
+    headers: T | {};
+    body: string;
+};
+
+export function networkAuthenticationRequired<T>(result: unknown, headers?: T): {
+    statusCode: 511;
+    headers: T | {};
+    body: string;
+};
+
+export function isContinue (response: unknown): boolean;
+
+export function isSwitchingProtocols (response: unknown): boolean;
+
+export function isProcessing (response: unknown): boolean;
+
+export function isOk (response: unknown): boolean;
+
+export function isCreated (response: unknown): boolean;
+
+export function isAccepted (response: unknown): boolean;
+
+export function isNonAuthoritativeInformation (response: unknown): boolean;
+
+export function isNoContent (response: unknown): boolean;
+
+export function isResetContent (response: unknown): boolean;
+
+export function isPartialContent (response: unknown): boolean;
+
+export function isMultiStatus (response: unknown): boolean;
+
+export function isMultipleChoices (response: unknown): boolean;
+
+export function isMovedPermanently (response: unknown): boolean;
+
+export function isMovedTemporarily (response: unknown): boolean;
+
+export function isSeeOther (response: unknown): boolean;
+
+export function isNotModified (response: unknown): boolean;
+
+export function isUseProxy (response: unknown): boolean;
+
+export function isTemporaryRedirect (response: unknown): boolean;
+
+export function isBadRequest (response: unknown): boolean;
+
+export function isUnauthorized (response: unknown): boolean;
+
+export function isPaymentRequired (response: unknown): boolean;
+
+export function isForbidden (response: unknown): boolean;
+
+export function isNotFound (response: unknown): boolean;
+
+export function isMethodNotAllowed (response: unknown): boolean;
+
+export function isNotAcceptable (response: unknown): boolean;
+
+export function isProxyAuthenticationRequired (response: unknown): boolean;
+
+export function isRequestTimeOut (response: unknown): boolean;
+
+export function isConflict (response: unknown): boolean;
+
+export function isGone (response: unknown): boolean;
+
+export function isLengthRequired (response: unknown): boolean;
+
+export function isPreconditionFailed (response: unknown): boolean;
+
+export function isRequestEntityTooLarge (response: unknown): boolean;
+
+export function isRequestUriTooLarge (response: unknown): boolean;
+
+export function isUnsupportedMediaType (response: unknown): boolean;
+
+export function isRequestedRangeNotSatisfiable (response: unknown): boolean;
+
+export function isExpectationFailed (response: unknown): boolean;
+
+export function isImATeapot (response: unknown): boolean;
+
+export function isUnprocessableEntity (response: unknown): boolean;
+
+export function isLocked (response: unknown): boolean;
+
+export function isFailedDependency (response: unknown): boolean;
+
+export function isUnorderedCollection (response: unknown): boolean;
+
+export function isUpgradeRequired (response: unknown): boolean;
+
+export function isPreconditionRequired (response: unknown): boolean;
+
+export function isTooManyRequests (response: unknown): boolean;
+
+export function isRequestHeaderFieldsTooLarge (response: unknown): boolean;
+
+export function isInternalServerError (response: unknown): boolean;
+
+export function isNotImplemented (response: unknown): boolean;
+
+export function isBadGateway (response: unknown): boolean;
+
+export function isServiceUnavailable (response: unknown): boolean;
+
+export function isGatewayTimeOut (response: unknown): boolean;
+
+export function isHttpVersionNotSupported (response: unknown): boolean;
+
+export function isVariantAlsoNegotiates (response: unknown): boolean;
+
+export function isInsufficientStorage (response: unknown): boolean;
+
+export function isBandwidthLimitExceeded (response: unknown): boolean;
+
+export function isNotExtended (response: unknown): boolean;
+
+export function isNetworkAuthenticationRequired (response: unknown): boolean;
\ No newline at end of file
diff --git a/index.esm.d.ts b/index.esm.d.ts
deleted file mode 100644
index 8a7a1fb..0000000
--- a/index.esm.d.ts
+++ /dev/null
@@ -1,331 +0,0 @@
-export function switchingProtocols(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function processing(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function ok(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function created(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function accepted(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function nonAuthoritativeInformation(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function noContent(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function resetContent(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function partialContent(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function multiStatus(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function multipleChoices(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function movedPermanently(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function movedTemporarily(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function seeOther(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function notModified(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function useProxy(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function temporaryRedirect(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function badRequest(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function unauthorized(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function paymentRequired(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function forbidden(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function notFound(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function methodNotAllowed(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function notAcceptable(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function proxyAuthenticationRequired(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function requestTimeOut(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function conflict(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function gone(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function lengthRequired(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function preconditionFailed(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function requestEntityTooLarge(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function requestUriTooLarge(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function unsupportedMediaType(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function requestedRangeNotSatisfiable(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function expectationFailed(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function imATeapot(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function unprocessableEntity(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function locked(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function failedDependency(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function unorderedCollection(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function upgradeRequired(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function preconditionRequired(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function tooManyRequests(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function requestHeaderFieldsTooLarge(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function internalServerError(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function notImplemented(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function badGateway(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function serviceUnavailable(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function gatewayTimeOut(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function httpVersionNotSupported(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function variantAlsoNegotiates(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function insufficientStorage(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function bandwidthLimitExceeded(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function notExtended(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function networkAuthenticationRequired(result: any, headers?: {}): {
-    statusCode: number;
-    headers: {};
-    body: string;
-};
-export function isContinue(response: any): boolean;
-export function isSwitchingProtocols(response: any): boolean;
-export function isProcessing(response: any): boolean;
-export function isOk(response: any): boolean;
-export function isCreated(response: any): boolean;
-export function isAccepted(response: any): boolean;
-export function isNonAuthoritativeInformation(response: any): boolean;
-export function isNoContent(response: any): boolean;
-export function isResetContent(response: any): boolean;
-export function isPartialContent(response: any): boolean;
-export function isMultiStatus(response: any): boolean;
-export function isMultipleChoices(response: any): boolean;
-export function isMovedPermanently(response: any): boolean;
-export function isMovedTemporarily(response: any): boolean;
-export function isSeeOther(response: any): boolean;
-export function isNotModified(response: any): boolean;
-export function isUseProxy(response: any): boolean;
-export function isTemporaryRedirect(response: any): boolean;
-export function isBadRequest(response: any): boolean;
-export function isUnauthorized(response: any): boolean;
-export function isPaymentRequired(response: any): boolean;
-export function isForbidden(response: any): boolean;
-export function isNotFound(response: any): boolean;
-export function isMethodNotAllowed(response: any): boolean;
-export function isNotAcceptable(response: any): boolean;
-export function isProxyAuthenticationRequired(response: any): boolean;
-export function isRequestTimeOut(response: any): boolean;
-export function isConflict(response: any): boolean;
-export function isGone(response: any): boolean;
-export function isLengthRequired(response: any): boolean;
-export function isPreconditionFailed(response: any): boolean;
-export function isRequestEntityTooLarge(response: any): boolean;
-export function isRequestUriTooLarge(response: any): boolean;
-export function isUnsupportedMediaType(response: any): boolean;
-export function isRequestedRangeNotSatisfiable(response: any): boolean;
-export function isExpectationFailed(response: any): boolean;
-export function isImATeapot(response: any): boolean;
-export function isUnprocessableEntity(response: any): boolean;
-export function isLocked(response: any): boolean;
-export function isFailedDependency(response: any): boolean;
-export function isUnorderedCollection(response: any): boolean;
-export function isUpgradeRequired(response: any): boolean;
-export function isPreconditionRequired(response: any): boolean;
-export function isTooManyRequests(response: any): boolean;
-export function isRequestHeaderFieldsTooLarge(response: any): boolean;
-export function isInternalServerError(response: any): boolean;
-export function isNotImplemented(response: any): boolean;
-export function isBadGateway(response: any): boolean;
-export function isServiceUnavailable(response: any): boolean;
-export function isGatewayTimeOut(response: any): boolean;
-export function isHttpVersionNotSupported(response: any): boolean;
-export function isVariantAlsoNegotiates(response: any): boolean;
-export function isInsufficientStorage(response: any): boolean;
-export function isBandwidthLimitExceeded(response: any): boolean;
-export function isNotExtended(response: any): boolean;
-export function isNetworkAuthenticationRequired(response: any): boolean;
diff --git a/index.esm.js b/index.js
similarity index 100%
rename from index.esm.js
rename to index.js
diff --git a/index.test.cjs b/index.test.cjs
deleted file mode 100644
index 3352657..0000000
--- a/index.test.cjs
+++ /dev/null
@@ -1,49 +0,0 @@
-describe('lambda-returns', () => {
-  let module;
-
-  beforeEach(() => {
-    module = require('./index');
-  });
-
-  test('length check', () => {
-    expect(Object.keys(module).length).toBe(111);
-  });
-
-  describe('some methods', () => {
-    test('ok', () => {
-      expect(module.ok({ status: 'success' })).toEqual({
-        statusCode: 200,
-        headers: {},
-        body: JSON.stringify({ status: 'success' }),
-      });
-    });
-
-    test('ok with headers', () => {
-      expect(module.ok({ status: 'success' }, { Content: 'json' })).toEqual({
-        statusCode: 200,
-        headers: {
-          Content: 'json',
-        },
-        body: JSON.stringify({ status: 'success' }),
-      });
-    });
-
-    test('noContent', () => {
-      expect(module.noContent()).toEqual({
-        statusCode: 204,
-        headers: {},
-        body: null,
-      });
-    });
-
-    test('badRequest', () => {
-      expect(
-        module.badRequest({ error: 'argument foo was not provided' })
-      ).toEqual({
-        statusCode: 400,
-        headers: {},
-        body: JSON.stringify({ error: 'argument foo was not provided' }),
-      });
-    });
-  });
-});
diff --git a/index.test.esm.js b/index.test.esm.js
deleted file mode 100644
index d92ca16..0000000
--- a/index.test.esm.js
+++ /dev/null
@@ -1,39 +0,0 @@
-import { ok, noContent, badRequest } from './index.esm.js';
-
-describe('lambda-returns', () => {
-  describe('some methods', () => {
-    test('ok', () => {
-      expect(ok({ status: 'success' })).toEqual({
-        statusCode: 200,
-        headers: {},
-        body: JSON.stringify({ status: 'success' }),
-      });
-    });
-
-    test('ok with headers', () => {
-      expect(ok({ status: 'success' }, { Content: 'json' })).toEqual({
-        statusCode: 200,
-        headers: {
-          Content: 'json',
-        },
-        body: JSON.stringify({ status: 'success' }),
-      });
-    });
-
-    test('noContent', () => {
-      expect(noContent()).toEqual({
-        statusCode: 204,
-        headers: {},
-        body: null,
-      });
-    });
-
-    test('badRequest', () => {
-      expect(badRequest({ error: 'argument foo was not provided' })).toEqual({
-        statusCode: 400,
-        headers: {},
-        body: JSON.stringify({ error: 'argument foo was not provided' }),
-      });
-    });
-  });
-});
diff --git a/index.test.js b/index.test.js
new file mode 100644
index 0000000..96a22eb
--- /dev/null
+++ b/index.test.js
@@ -0,0 +1,259 @@
+import * as lambdaReturns from './index.js';
+import codes from './codes.js';
+import capitalizeFirstLetter from './src/capitalize_first/index.js';
+import randomInteger from './src/random_integer/index.js';
+
+describe('lambda-returns', () => {
+  const codesEntries = Object.entries(codes);
+
+  describe('basic methods', () => {
+    // can't test continue status word because it's forbidden to export it in JS
+    // look at README
+    const cases = codesEntries
+      .filter(([status]) => status !== 'continue')
+      .map(([status, code]) => [status, code]);
+
+    test.each(cases)('%s should return %s when empty args', (status, code) => {
+      expect(lambdaReturns[status]()).toEqual({
+        statusCode: code,
+        headers: {},
+        body: null,
+      });
+    });
+
+    test.each(cases)(
+      '%s should return %s when empty body but headers filled',
+      (status, code) => {
+        expect(
+          lambdaReturns[status](undefined, { ContentType: 'application/json' })
+        ).toEqual({
+          statusCode: code,
+          headers: { ContentType: 'application/json' },
+          body: null,
+        });
+      }
+    );
+
+    test.each(cases)(
+      '%s should return %s when has obect body, no headers',
+      (status, code) => {
+        expect(lambdaReturns[status]({ status: 'success' })).toEqual({
+          statusCode: code,
+          headers: {},
+          body: '{"status":"success"}',
+        });
+      }
+    );
+
+    test.each(cases)(
+      '%s should return %s when has string body, no headers',
+      (status, code) => {
+        expect(lambdaReturns[status]('{"everything":"is good"}')).toEqual({
+          statusCode: code,
+          headers: {},
+          body: '{"everything":"is good"}',
+        });
+      }
+    );
+
+    test.each(cases)(
+      '%s should return %s when has obect body, with headers',
+      (status, code) => {
+        expect(
+          lambdaReturns[status](
+            { status: 'success' },
+            {
+              'Accept-Encoding': 'gzip, deflate, br',
+            }
+          )
+        ).toEqual({
+          statusCode: code,
+          headers: {
+            'Accept-Encoding': 'gzip, deflate, br',
+          },
+          body: '{"status":"success"}',
+        });
+      }
+    );
+
+    test.each(cases)(
+      '%s should return %s when has string body, with headers',
+      (status, code) => {
+        expect(
+          lambdaReturns[status]('{"everything":"is good"}', {
+            'Cache-Control': 'no-cache',
+          })
+        ).toEqual({
+          statusCode: code,
+          headers: {
+            'Cache-Control': 'no-cache',
+          },
+          body: '{"everything":"is good"}',
+        });
+      }
+    );
+  });
+
+  describe('test helper methods', () => {
+    const cases = codesEntries.map(([status, code]) => [
+      `is${capitalizeFirstLetter(status)}`,
+      code,
+    ]);
+
+    test.each(cases)(
+      '%s should return %s when empty body, empty headers',
+      (statusTest, code) => {
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: code,
+            headers: {},
+            body: null,
+          })
+        ).toBe(true);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: {},
+            body: null,
+          })
+        ).toBe(false);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: {},
+            body: null,
+          })
+        ).toBe(false);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: {},
+            body: null,
+          })
+        ).toBe(false);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: {},
+            body: null,
+          })
+        ).toBe(false);
+      }
+    );
+
+    test.each(cases)(
+      '%s should return %s when has body',
+      (statusTest, code) => {
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: code,
+            headers: {},
+            body: '{"status":"success"}',
+          })
+        ).toBe(true);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: {},
+            body: '{"status":"success"}',
+          })
+        ).toBe(false);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: {},
+            body: '{"status":"success"}',
+          })
+        ).toBe(false);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: {},
+            body: '{"status":"success"}',
+          })
+        ).toBe(false);
+      }
+    );
+
+    test.each(cases)(
+      '%s should return %s when has body and headers',
+      (statusTest, code) => {
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: code,
+            headers: { ContentType: 'application/json' },
+            body: '{"status":"success"}',
+          })
+        ).toBe(true);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: { ContentType: 'application/json' },
+            body: '{"status":"success"}',
+          })
+        ).toBe(false);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: { ContentType: 'application/json' },
+            body: '{"status":"success"}',
+          })
+        ).toBe(false);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: { ContentType: 'application/json' },
+            body: '{"status":"success"}',
+          })
+        ).toBe(false);
+      }
+    );
+
+    test.each(cases)(
+      '%s should return %s when has headers and no body',
+      (statusTest, code) => {
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: code,
+            headers: { ContentType: 'application/json' },
+            body: null,
+          })
+        ).toBe(true);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: { ContentType: 'application/json' },
+            body: null,
+          })
+        ).toBe(false);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: { ContentType: 'application/json' },
+            body: null,
+          })
+        ).toBe(false);
+
+        expect(
+          lambdaReturns[statusTest]({
+            statusCode: randomInteger(code),
+            headers: { ContentType: 'application/json' },
+            body: null,
+          })
+        ).toBe(false);
+      }
+    );
+  });
+});
diff --git a/jest.config.cjs b/jest.config.cjs
deleted file mode 100644
index 4becb1f..0000000
--- a/jest.config.cjs
+++ /dev/null
@@ -1,14 +0,0 @@
-/*
- * For a detailed explanation regarding each configuration property, visit:
- * https://jestjs.io/docs/configuration
- */
-
-module.exports = {
-  clearMocks: true,
-  collectCoverage: true,
-  coverageDirectory: "coverage",
-  coverageProvider: "v8",
-  testMatch: [
-    "**/index.test.cjs"
-  ]
-};
diff --git a/jest.config.esm.js b/jest.config.js
similarity index 60%
rename from jest.config.esm.js
rename to jest.config.js
index 7811f37..ad5e51e 100644
--- a/jest.config.esm.js
+++ b/jest.config.js
@@ -4,11 +4,11 @@
  */
 
 export default {
+  bail: true,
+  transform: {},
   clearMocks: true,
   collectCoverage: true,
-  coverageDirectory: "coverage",
-  coverageProvider: "v8",
-  testMatch: [
-    "**/index.test.esm.js"
-  ]
+  coverageDirectory: 'coverage',
+  coverageProvider: 'v8',
+  testMatch: ['**/index.test.js'],
 };
diff --git a/package.json b/package.json
index 0b8644a..6ffa328 100644
--- a/package.json
+++ b/package.json
@@ -1,9 +1,9 @@
 {
   "name": "lambda-returns",
-  "version": "2.2.1",
+  "version": "3.0.1",
   "main": "index.cjs",
-  "module": "index.esm.js",
-  "types": "./index.esm.d.ts",
+  "module": "index.js",
+  "types": "./index.d.ts",
   "repository": "git@github.com:MathRobin/lambda-returns.git",
   "author": "MathRobin <mthrobin@gmail.com>",
   "license": "MIT",
@@ -11,13 +11,13 @@
   "packageManager": "yarn@3.6.4",
   "type": "module",
   "scripts": {
-    "build": "node build.js; npx -p typescript tsc ./index.esm.js --declaration --allowJs --emitDeclarationOnly --outDir .",
+    "build": "yarn build:source && yarn build:typings",
+    "build:source": "node build.js",
+    "build:typings": "node typings.js",
     "lint": "eslint .",
-    "testCjs": "jest --coverage -c jest.config.cjs --coverageDirectory coverage_cjs",
-    "testEsm": "NODE_OPTIONS=--experimental-vm-modules npx jest --coverage -c jest.config.esm.js",
     "pretest": "yarn build",
     "publish": "yarn build && yarn npm publish && git add package.json yarn.lock",
-    "test": "yarn testCjs; yarn testEsm",
+    "test": "NODE_OPTIONS=--experimental-vm-modules npx jest --coverage -c jest.config.js",
     "prepare": "husky install"
   },
   "devDependencies": {
@@ -27,7 +27,6 @@
     "eslint-plugin-jest": "27.4.2",
     "husky": "8.0.3",
     "jest": "29.7.0",
-    "prettier": "3.0.3",
-    "typescript": "5.2.2"
+    "prettier": "3.0.3"
   }
 }
diff --git a/src/capitalize_first/index.js b/src/capitalize_first/index.js
new file mode 100644
index 0000000..0437931
--- /dev/null
+++ b/src/capitalize_first/index.js
@@ -0,0 +1,3 @@
+export default function capitalizeFirstLetter(string) {
+  return string[0].toUpperCase() + string.slice(1);
+}
diff --git a/src/random_integer/index.js b/src/random_integer/index.js
new file mode 100644
index 0000000..4a03464
--- /dev/null
+++ b/src/random_integer/index.js
@@ -0,0 +1,9 @@
+export default function randomInteger(codeExcluded, min = 100, max = 511) {
+  let result;
+
+  do {
+    result = Math.floor(Math.random() * (max - min + 1)) + min;
+  } while (result === codeExcluded);
+
+  return result;
+}
diff --git a/src/random_integer/index.test.js b/src/random_integer/index.test.js
new file mode 100644
index 0000000..688cefd
--- /dev/null
+++ b/src/random_integer/index.test.js
@@ -0,0 +1,25 @@
+import randomInteger from './index.js';
+
+describe('randomInteger', () => {
+  const cases = [
+    [randomInteger(2, 1, 2), 1, 2, 2],
+    [randomInteger(2, 1, 2), 1, 2, 2],
+    [randomInteger(2, 1, 2), 1, 2, 2],
+    [randomInteger(2, 1, 2), 1, 2, 2],
+    [randomInteger(2, 1, 2), 1, 2, 2],
+    [randomInteger(2, 1, 2), 1, 2, 2],
+    [randomInteger(200), 100, 511, 200],
+    [randomInteger(200, 100), 100, 511, 200],
+    [randomInteger(200, 100, 511), 100, 511, 200],
+    [randomInteger(200, undefined, 511), 100, 511, 200],
+  ];
+
+  test.each(cases)(
+    '%s is between %s and %s (both included)',
+    (codeExcluded, min, max, codeAsked) => {
+      expect(codeExcluded).toBeGreaterThanOrEqual(min);
+      expect(codeExcluded).toBeLessThanOrEqual(max);
+      expect(codeExcluded).not.toBe(codeAsked);
+    }
+  );
+});
diff --git a/typings.js b/typings.js
new file mode 100644
index 0000000..1e507f1
--- /dev/null
+++ b/typings.js
@@ -0,0 +1,34 @@
+import fs from 'fs';
+
+import codes from './codes.js';
+
+const exportsEsm = [];
+
+function capitalizeFirstLetter(string) {
+  return string[0].toUpperCase() + string.slice(1);
+}
+
+Object.entries(codes)
+  .filter(([message]) => {
+    // can't be exported as it uses a reserved word
+    return message !== 'continue';
+  })
+  .forEach(([message, code]) => {
+    exportsEsm.push(`export function ${message}<T>(result: unknown, headers?: T): {
+    statusCode: ${code};
+    headers: T | {};
+    body: string;
+};`);
+  });
+
+Object.entries(codes).forEach(([message]) => {
+  exportsEsm.push(
+    `export function is${capitalizeFirstLetter(
+      message
+    )} (response: unknown): boolean;`
+  );
+});
+
+fs.writeFile('./index.d.ts', exportsEsm.join('\n\n'), () => {
+  console.log('Module typings generated');
+});
diff --git a/yarn.lock b/yarn.lock
index 0f553b2..a95d022 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3181,7 +3181,6 @@ __metadata:
     husky: 8.0.3
     jest: 29.7.0
     prettier: 3.0.3
-    typescript: 5.2.2
   languageName: unknown
   linkType: soft
 
@@ -4304,26 +4303,6 @@ __metadata:
   languageName: node
   linkType: hard
 
-"typescript@npm:5.2.2":
-  version: 5.2.2
-  resolution: "typescript@npm:5.2.2"
-  bin:
-    tsc: bin/tsc
-    tsserver: bin/tsserver
-  checksum: 7912821dac4d962d315c36800fe387cdc0a6298dba7ec171b350b4a6e988b51d7b8f051317786db1094bd7431d526b648aba7da8236607febb26cf5b871d2d3c
-  languageName: node
-  linkType: hard
-
-"typescript@patch:typescript@5.2.2#~builtin<compat/typescript>":
-  version: 5.2.2
-  resolution: "typescript@patch:typescript@npm%3A5.2.2#~builtin<compat/typescript>::version=5.2.2&hash=f3b441"
-  bin:
-    tsc: bin/tsc
-    tsserver: bin/tsserver
-  checksum: 0f4da2f15e6f1245e49db15801dbee52f2bbfb267e1c39225afdab5afee1a72839cd86000e65ee9d7e4dfaff12239d28beaf5ee431357fcced15fb08583d72ca
-  languageName: node
-  linkType: hard
-
 "unique-filename@npm:^3.0.0":
   version: 3.0.0
   resolution: "unique-filename@npm:3.0.0"