diff --git a/.eslintrc.json b/.eslintrc.json
index b6d7249e..c6c74370 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -59,6 +59,8 @@
                 "@typescript-eslint/prefer-includes": 2,
                 "@typescript-eslint/switch-exhaustiveness-check": 2,
 
+                "dot-notation": 0,
+
                 "jsdoc/require-param-type": 0,
                 "jsdoc/require-returns-type": 0
             }
diff --git a/package.json b/package.json
index b4edcead..460523d8 100644
--- a/package.json
+++ b/package.json
@@ -10,6 +10,11 @@
     "sideEffects": false,
     "main": "lib/index.js",
     "types": "lib/index.d.ts",
+    "module": "lib/esm/index.js",
+    "exports": {
+        "require": "./lib/index.js",
+        "import": "./lib/esm/index.js"
+    },
     "files": [
         "lib/**/*"
     ],
@@ -23,8 +28,9 @@
         "format:es": "npm run lint:es -- --fix",
         "format:prettier": "npm run prettier -- --write",
         "prettier": "prettier \"**/*.{ts,md,json,yml}\" --ignore-path .gitignore",
-        "build": "tsc",
-        "build:docs": "typedoc --hideGenerator --exclude \"**/*+(index|.spec).ts\" --categorizeByGroup false --sort enum-value-ascending --sort alphabetical src",
+        "build": "npm run build:cjs && npm run build:esm",
+        "build:cjs": "tsc --sourceRoot https://raw.githubusercontent.com/fb55/domutils/$(git rev-parse HEAD)/src/",
+        "build:esm": "npm run build:cjs -- --module esnext --target es2019 --outDir lib/esm && echo '{\"type\":\"module\"}' > lib/esm/package.json",
         "prepare": "npm run build"
     },
     "repository": {
@@ -57,7 +63,11 @@
     },
     "jest": {
         "preset": "ts-jest",
-        "testEnvironment": "node"
+        "testEnvironment": "node",
+        "coverageProvider": "v8",
+        "moduleNameMapper": {
+            "^(.*)\\.js$": "$1"
+        }
     },
     "prettier": {
         "tabWidth": 4
diff --git a/src/feeds.ts b/src/feeds.ts
index 2f25f2e5..8e942bde 100644
--- a/src/feeds.ts
+++ b/src/feeds.ts
@@ -1,6 +1,6 @@
 import type { AnyNode, Element } from "domhandler";
-import { textContent } from "./stringify";
-import { getElementsByTagName } from "./legacy";
+import { textContent } from "./stringify.js";
+import { getElementsByTagName } from "./legacy.js";
 
 /**
  * The type of a media item.
@@ -108,7 +108,7 @@ function getAtomFeed(feedRoot: Element) {
             addConditionally(entry, "id", "id", children);
             addConditionally(entry, "title", "title", children);
 
-            const href = getOneElement("link", children)?.attribs.href;
+            const href = getOneElement("link", children)?.attribs["href"];
             if (href) {
                 entry.link = href;
             }
@@ -130,7 +130,7 @@ function getAtomFeed(feedRoot: Element) {
 
     addConditionally(feed, "id", "id", childs);
     addConditionally(feed, "title", "title", childs);
-    const href = getOneElement("link", childs)?.attribs.href;
+    const href = getOneElement("link", childs)?.attribs["href"];
     if (href) {
         feed.link = href;
     }
@@ -211,10 +211,10 @@ function getMediaElements(where: AnyNode[]): FeedItemMedia[] {
         const { attribs } = elem;
 
         const media: FeedItemMedia = {
-            medium: attribs.medium as unknown as
+            medium: attribs["medium"] as unknown as
                 | FeedItemMediaMedium
                 | undefined,
-            isDefault: !!attribs.isDefault,
+            isDefault: !!attribs["isDefault"],
         };
 
         for (const attrib of MEDIA_KEYS_STRING) {
@@ -229,9 +229,10 @@ function getMediaElements(where: AnyNode[]): FeedItemMedia[] {
             }
         }
 
-        if (attribs.expression) {
-            media.expression =
-                attribs.expression as unknown as FeedItemMediaExpression;
+        if (attribs["expression"]) {
+            media.expression = attribs[
+                "expression"
+            ] as unknown as FeedItemMediaExpression;
         }
 
         return media;
diff --git a/src/index.ts b/src/index.ts
index 9a236944..6ecab3b3 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,10 +1,10 @@
-export * from "./stringify";
-export * from "./traversal";
-export * from "./manipulation";
-export * from "./querying";
-export * from "./legacy";
-export * from "./helpers";
-export * from "./feeds";
+export * from "./stringify.js";
+export * from "./traversal.js";
+export * from "./manipulation.js";
+export * from "./querying.js";
+export * from "./legacy.js";
+export * from "./helpers.js";
+export * from "./feeds.js";
 /** @deprecated Use these methods from `domhandler` directly. */
 export {
     isTag,
diff --git a/src/legacy.ts b/src/legacy.ts
index 9aac19ff..5449d889 100644
--- a/src/legacy.ts
+++ b/src/legacy.ts
@@ -1,6 +1,6 @@
 import { isTag, isText, AnyNode, Element } from "domhandler";
-import { ElementType } from "domelementtype";
-import { filter, findOne } from "./querying";
+import type { ElementType } from "domelementtype";
+import { filter, findOne } from "./querying.js";
 
 type TestType = (elem: AnyNode) => boolean;
 
@@ -148,7 +148,12 @@ export function getElementsByTagName(
     recurse = true,
     limit = Infinity
 ): Element[] {
-    return filter(Checks.tag_name(tagName), nodes, recurse, limit) as Element[];
+    return filter(
+        Checks["tag_name"](tagName),
+        nodes,
+        recurse,
+        limit
+    ) as Element[];
 }
 
 /**
@@ -165,5 +170,5 @@ export function getElementsByTagType(
     recurse = true,
     limit = Infinity
 ): AnyNode[] {
-    return filter(Checks.tag_type(type as string), nodes, recurse, limit);
+    return filter(Checks["tag_type"](type as string), nodes, recurse, limit);
 }
diff --git a/tsconfig.json b/tsconfig.json
index 5d16dc75..045b82d5 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,27 +1,32 @@
 {
     "compilerOptions": {
         /* Basic Options */
-        "target": "es5" /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019' or 'ESNEXT'. */,
-        "module": "commonjs" /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */,
-        // "lib": [],                             /* Specify library files to be included in the compilation. */
-        "declaration": true /* Generates corresponding '.d.ts' file. */,
-        "declarationMap": true /* Generates a sourcemap for each corresponding '.d.ts' file. */,
-        // "sourceMap": true,                     /* Generates corresponding '.map' file. */
-        "outDir": "lib" /* Redirect output structure to the directory. */,
-        // "importHelpers": true,                 /* Import emit helpers from 'tslib'. */
+        "target": "es5",
+        "module": "commonjs",
+        "lib": ["ES2015.Core"],
+        "declaration": true,
+        "declarationMap": true,
+        "sourceMap": true,
+        "outDir": "lib",
 
         /* Strict Type-Checking Options */
-        "strict": true /* Enable all strict type-checking options. */,
+        "strict": true,
 
         /* Additional Checks */
-        "noUnusedLocals": true /* Report errors on unused locals. */,
-        "noUnusedParameters": true /* Report errors on unused parameters. */,
-        "noImplicitReturns": true /* Report error when not all code paths in function return a value. */,
-        "noFallthroughCasesInSwitch": true /* Report errors for fallthrough cases in switch statement. */,
+        "exactOptionalPropertyTypes": true,
+        "forceConsistentCasingInFileNames": true,
+        "importsNotUsedAsValues": "error",
+        "isolatedModules": true,
+        "noFallthroughCasesInSwitch": true,
+        "noImplicitOverride": true,
+        "noImplicitReturns": true,
+        "noPropertyAccessFromIndexSignature": true,
+        "noUnusedLocals": true,
+        "noUnusedParameters": true,
 
         /* Module Resolution Options */
-        // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
-        "esModuleInterop": true /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */,
+        "esModuleInterop": true,
+        "moduleResolution": "node",
         "resolveJsonModule": true
     },
     "include": ["src"],