diff --git a/lib/lock.js b/lib/lock.js
index fc5eb1f..2851a5e 100644
--- a/lib/lock.js
+++ b/lib/lock.js
@@ -13,6 +13,12 @@ const assert = require('bsert');
  */
 
 class Lock {
+  /** @type {Boolean} */
+  named;
+
+  /** @type {Map} */
+  map;
+
   /**
    * Create a lock.
    * @constructor
@@ -30,6 +36,7 @@ class Lock {
     this.busy = false;
     this.destroyed = false;
 
+    // @ts-ignore
     this.map = CustomMap ? new CustomMap() : new Map();
     this.current = null;
 
@@ -94,9 +101,9 @@ class Lock {
   /**
    * Lock the parent object and all its methods
    * which use the lock. Begin to queue calls.
-   * @param {String?} name - Job name.
-   * @param {Boolean?} force - Bypass the lock.
-   * @returns {Promise} - Returns {Function}, must be
+   * @param {String|Boolean} [arg1] - Job name or bypass the lock.
+   * @param {Boolean} [arg2=false] - Bypass the lock.
+   * @returns {Promise<Function>} - Returns {Function}, must be
    * called once the method finishes executing in order
    * to resolve the queue.
    */
@@ -201,7 +208,7 @@ class Job {
    * @constructor
    * @param {Function} resolve
    * @param {Function} reject
-   * @param {String?} name
+   * @param {String} [name]
    */
 
   constructor(resolve, reject, name) {
diff --git a/lib/maplock.js b/lib/maplock.js
index c9361d9..ce892a8 100644
--- a/lib/maplock.js
+++ b/lib/maplock.js
@@ -13,6 +13,12 @@ const assert = require('bsert');
  */
 
 class MapLock {
+  /** @type {Map} */
+  jobs;
+
+  /** @type {Set} */
+  busy;
+
   /**
    * Create a mapped lock.
    * @param {Function?} CustomMap
@@ -27,7 +33,9 @@ class MapLock {
     this.Map = CustomMap || Map;
     this.Set = CustomSet || Set;
 
+    // @ts-ignore
     this.jobs = new this.Map();
+    // @ts-ignore
     this.busy = new this.Set();
 
     this.destroyed = false;
@@ -75,7 +83,7 @@ class MapLock {
    * Begin to queue calls.
    * @param {String|Number} key
    * @param {Boolean} [force=false] - Force a call.
-   * @returns {Promise} - Returns {Function}, must be
+   * @returns {Promise<Function>} - Returns {Function}, must be
    * called once the method finishes executing in order
    * to resolve the queue.
    */
@@ -108,7 +116,7 @@ class MapLock {
   /**
    * Create an unlock callback.
    * @private
-   * @param {String} key
+   * @param {String|Number} key
    * @returns {Function} Unlocker.
    */
 
@@ -159,7 +167,9 @@ class MapLock {
 
     this.destroyed = true;
 
+    // @ts-ignore
     this.jobs = new this.Map();
+    // @ts-ignore
     this.busy = new this.Set();
 
     for (const jobs of map.values()) {
diff --git a/package-lock.json b/package-lock.json
index b6ebf8c..e491323 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -9,10 +9,11 @@
       "version": "0.1.6",
       "license": "MIT",
       "dependencies": {
-        "bsert": "~0.0.10"
+        "bsert": "~0.0.12"
       },
       "devDependencies": {
-        "bmocha": "^2.1.0"
+        "bmocha": "^2.1.8",
+        "bts-type-deps": "^0.0.3"
       },
       "engines": {
         "node": ">=8.0.0"
@@ -38,6 +39,12 @@
       "engines": {
         "node": ">=8.0.0"
       }
+    },
+    "node_modules/bts-type-deps": {
+      "version": "0.0.3",
+      "resolved": "https://registry.npmjs.org/bts-type-deps/-/bts-type-deps-0.0.3.tgz",
+      "integrity": "sha512-OQHGWhX5amae6Vj6ShlGaQu0sNCICgJ5YspNZPRzfR5RobrD+wjm5vkZK/J3EH5b/ymxqSWo9VkiFNpCxjaG2Q==",
+      "dev": true
     }
   }
 }
diff --git a/package.json b/package.json
index 01d74b6..ebee65a 100644
--- a/package.json
+++ b/package.json
@@ -16,13 +16,15 @@
   "main": "./lib/bmutex.js",
   "scripts": {
     "lint": "eslint lib/ test/",
+    "lint-types": "tsc -p .",
     "test": "bmocha --reporter spec test/*-test.js"
   },
   "dependencies": {
-    "bsert": "~0.0.10"
+    "bsert": "~0.0.12"
   },
   "devDependencies": {
-    "bmocha": "^2.1.0"
+    "bmocha": "^2.1.8",
+    "bts-type-deps": "^0.0.3"
   },
   "engines": {
     "node": ">=8.0.0"
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..da7a94b
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,31 @@
+{
+  "include": [
+    "lib/**/*.js"
+  ],
+  "compilerOptions": {
+    "rootDir": ".",
+    "target": "ES2020",
+    "lib": [
+      "ES2020"
+    ],
+
+    "noEmit": true,
+
+    "allowJs": true,
+    "checkJs": true,
+    "maxNodeModuleJsDepth": 10,
+
+    "module": "commonjs",
+    "moduleResolution": "node",
+    "resolveJsonModule": true,
+
+    "stripInternal": true,
+    "noImplicitThis": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": false,
+
+    "typeRoots": [
+      "node_modules/bts-type-deps/types"
+    ]
+  }
+}