diff --git a/package-lock.json b/package-lock.json
index 94dd461..c2c6612 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "@msgpack/msgpack",
-  "version": "3.0.0-beta2",
+  "version": "3.0.0-beta3",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@msgpack/msgpack",
-      "version": "3.0.0-beta2",
+      "version": "3.0.0-beta3",
       "license": "ISC",
       "devDependencies": {
         "@bitjourney/check-es-version-webpack-plugin": "latest",
@@ -777,18 +777,17 @@
         "typescript": ">=4.8.4 <5.8.0"
       }
     },
-    "node_modules/@typescript-eslint/parser": {
+    "node_modules/@typescript-eslint/eslint-plugin/node_modules/@typescript-eslint/type-utils": {
       "version": "8.21.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/parser/-/parser-8.21.0.tgz",
-      "integrity": "sha512-Wy+/sdEH9kI3w9civgACwabHbKl+qIOu0uFZ9IMKzX3Jpv9og0ZBJrZExGrPpFAY7rWsXuxs5e7CPPP17A4eYA==",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/type-utils/-/type-utils-8.21.0.tgz",
+      "integrity": "sha512-95OsL6J2BtzoBxHicoXHxgk3z+9P3BEcQTpBKriqiYzLKnM2DeSqs+sndMKdamU8FosiadQFT3D+BSL9EKnAJQ==",
       "dev": true,
       "license": "MIT",
       "dependencies": {
-        "@typescript-eslint/scope-manager": "8.21.0",
-        "@typescript-eslint/types": "8.21.0",
         "@typescript-eslint/typescript-estree": "8.21.0",
-        "@typescript-eslint/visitor-keys": "8.21.0",
-        "debug": "^4.3.4"
+        "@typescript-eslint/utils": "8.21.0",
+        "debug": "^4.3.4",
+        "ts-api-utils": "^2.0.0"
       },
       "engines": {
         "node": "^18.18.0 || ^20.9.0 || >=21.1.0"
@@ -802,15 +801,17 @@
         "typescript": ">=4.8.4 <5.8.0"
       }
     },
-    "node_modules/@typescript-eslint/scope-manager": {
+    "node_modules/@typescript-eslint/eslint-plugin/node_modules/@typescript-eslint/utils": {
       "version": "8.21.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/scope-manager/-/scope-manager-8.21.0.tgz",
-      "integrity": "sha512-G3IBKz0/0IPfdeGRMbp+4rbjfSSdnGkXsM/pFZA8zM9t9klXDnB/YnKOBQ0GoPmoROa4bCq2NeHgJa5ydsQ4mA==",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/utils/-/utils-8.21.0.tgz",
+      "integrity": "sha512-xcXBfcq0Kaxgj7dwejMbFyq7IOHgpNMtVuDveK7w3ZGwG9owKzhALVwKpTF2yrZmEwl9SWdetf3fxNzJQaVuxw==",
       "dev": true,
       "license": "MIT",
       "dependencies": {
+        "@eslint-community/eslint-utils": "^4.4.0",
+        "@typescript-eslint/scope-manager": "8.21.0",
         "@typescript-eslint/types": "8.21.0",
-        "@typescript-eslint/visitor-keys": "8.21.0"
+        "@typescript-eslint/typescript-estree": "8.21.0"
       },
       "engines": {
         "node": "^18.18.0 || ^20.9.0 || >=21.1.0"
@@ -818,19 +819,24 @@
       "funding": {
         "type": "opencollective",
         "url": "https://opencollective.com/typescript-eslint"
+      },
+      "peerDependencies": {
+        "eslint": "^8.57.0 || ^9.0.0",
+        "typescript": ">=4.8.4 <5.8.0"
       }
     },
-    "node_modules/@typescript-eslint/type-utils": {
+    "node_modules/@typescript-eslint/parser": {
       "version": "8.21.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/type-utils/-/type-utils-8.21.0.tgz",
-      "integrity": "sha512-95OsL6J2BtzoBxHicoXHxgk3z+9P3BEcQTpBKriqiYzLKnM2DeSqs+sndMKdamU8FosiadQFT3D+BSL9EKnAJQ==",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/parser/-/parser-8.21.0.tgz",
+      "integrity": "sha512-Wy+/sdEH9kI3w9civgACwabHbKl+qIOu0uFZ9IMKzX3Jpv9og0ZBJrZExGrPpFAY7rWsXuxs5e7CPPP17A4eYA==",
       "dev": true,
       "license": "MIT",
       "dependencies": {
+        "@typescript-eslint/scope-manager": "8.21.0",
+        "@typescript-eslint/types": "8.21.0",
         "@typescript-eslint/typescript-estree": "8.21.0",
-        "@typescript-eslint/utils": "8.21.0",
-        "debug": "^4.3.4",
-        "ts-api-utils": "^2.0.0"
+        "@typescript-eslint/visitor-keys": "8.21.0",
+        "debug": "^4.3.4"
       },
       "engines": {
         "node": "^18.18.0 || ^20.9.0 || >=21.1.0"
@@ -844,6 +850,24 @@
         "typescript": ">=4.8.4 <5.8.0"
       }
     },
+    "node_modules/@typescript-eslint/scope-manager": {
+      "version": "8.21.0",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/scope-manager/-/scope-manager-8.21.0.tgz",
+      "integrity": "sha512-G3IBKz0/0IPfdeGRMbp+4rbjfSSdnGkXsM/pFZA8zM9t9klXDnB/YnKOBQ0GoPmoROa4bCq2NeHgJa5ydsQ4mA==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@typescript-eslint/types": "8.21.0",
+        "@typescript-eslint/visitor-keys": "8.21.0"
+      },
+      "engines": {
+        "node": "^18.18.0 || ^20.9.0 || >=21.1.0"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/typescript-eslint"
+      }
+    },
     "node_modules/@typescript-eslint/types": {
       "version": "8.21.0",
       "resolved": "https://registry.npmjs.org/@typescript-eslint/types/-/types-8.21.0.tgz",
@@ -885,30 +909,6 @@
         "typescript": ">=4.8.4 <5.8.0"
       }
     },
-    "node_modules/@typescript-eslint/utils": {
-      "version": "8.21.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/utils/-/utils-8.21.0.tgz",
-      "integrity": "sha512-xcXBfcq0Kaxgj7dwejMbFyq7IOHgpNMtVuDveK7w3ZGwG9owKzhALVwKpTF2yrZmEwl9SWdetf3fxNzJQaVuxw==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "@eslint-community/eslint-utils": "^4.4.0",
-        "@typescript-eslint/scope-manager": "8.21.0",
-        "@typescript-eslint/types": "8.21.0",
-        "@typescript-eslint/typescript-estree": "8.21.0"
-      },
-      "engines": {
-        "node": "^18.18.0 || ^20.9.0 || >=21.1.0"
-      },
-      "funding": {
-        "type": "opencollective",
-        "url": "https://opencollective.com/typescript-eslint"
-      },
-      "peerDependencies": {
-        "eslint": "^8.57.0 || ^9.0.0",
-        "typescript": ">=4.8.4 <5.8.0"
-      }
-    },
     "node_modules/@typescript-eslint/visitor-keys": {
       "version": "8.21.0",
       "resolved": "https://registry.npmjs.org/@typescript-eslint/visitor-keys/-/visitor-keys-8.21.0.tgz",
@@ -3004,9 +3004,9 @@
       }
     },
     "node_modules/fastq": {
-      "version": "1.18.0",
-      "resolved": "https://registry.npmjs.org/fastq/-/fastq-1.18.0.tgz",
-      "integrity": "sha512-QKHXPW0hD8g4UET03SdOdunzSouc9N4AuHdsX8XNcTsuz+yYFILVNIX4l9yHABMhiEI9Db0JTTIpu0wB+Y1QQw==",
+      "version": "1.19.0",
+      "resolved": "https://registry.npmjs.org/fastq/-/fastq-1.19.0.tgz",
+      "integrity": "sha512-7SFSRCNjBQIZH/xZR3iy5iQYR8aGBE0h3VG6/cwlbrpdciNYBMotQav8c1XI3HjHH+NikUpP53nPdlZSdWmFzA==",
       "dev": true,
       "license": "ISC",
       "dependencies": {
@@ -5920,9 +5920,9 @@
       }
     },
     "node_modules/semver": {
-      "version": "7.6.3",
-      "resolved": "https://registry.npmjs.org/semver/-/semver-7.6.3.tgz",
-      "integrity": "sha512-oVekP1cKtI+CTDvHWYFUcMtsK/00wmAEfyqKfNdARm8u1wNVhSgaX7A8d4UuIlUI5e84iEwOhs7ZPYRmzU9U6A==",
+      "version": "7.7.0",
+      "resolved": "https://registry.npmjs.org/semver/-/semver-7.7.0.tgz",
+      "integrity": "sha512-DrfFnPzblFmNrIZzg5RzHegbiRWg7KMR7btwi2yjHwx06zsUbO5g613sVwEV7FTwmzJu+Io0lJe2GJ3LxqpvBQ==",
       "dev": true,
       "license": "ISC",
       "bin": {
diff --git a/src/CachedKeyDecoder.ts b/src/CachedKeyDecoder.ts
index b57c222..0dfb2eb 100644
--- a/src/CachedKeyDecoder.ts
+++ b/src/CachedKeyDecoder.ts
@@ -16,11 +16,16 @@ export class CachedKeyDecoder implements KeyDecoder {
   hit = 0;
   miss = 0;
   private readonly caches: Array<Array<KeyCacheRecord>>;
+  private readonly maxKeyLength: number;
+  private readonly maxLengthPerKey: number;
 
   constructor(
-    readonly maxKeyLength = DEFAULT_MAX_KEY_LENGTH,
-    readonly maxLengthPerKey = DEFAULT_MAX_LENGTH_PER_KEY,
+    maxKeyLength = DEFAULT_MAX_KEY_LENGTH,
+    maxLengthPerKey = DEFAULT_MAX_LENGTH_PER_KEY,
   ) {
+    this.maxKeyLength = maxKeyLength;
+    this.maxLengthPerKey = maxLengthPerKey;
+
     // avoid `new Array(N)`, which makes a sparse array,
     // because a sparse array is typically slower than a non-sparse array.
     this.caches = [];
diff --git a/src/ExtData.ts b/src/ExtData.ts
index facdddc..fd56fc1 100644
--- a/src/ExtData.ts
+++ b/src/ExtData.ts
@@ -2,8 +2,14 @@
  * ExtData is used to handle Extension Types that are not registered to ExtensionCodec.
  */
 export class ExtData {
+  readonly type: number;
+  readonly data: Uint8Array;
+
   constructor(
-    readonly type: number,
-    readonly data: Uint8Array,
-  ) {}
+    type: number,
+    data: Uint8Array,
+  ) {
+    this.type = type;
+    this.data = data;
+  }
 }
diff --git a/tsconfig.json b/tsconfig.json
index 703957f..c62b0b1 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -56,6 +56,8 @@
     // "preserveSymlinks": true,              /* Do not resolve the real path of symlinks. */
     "forceConsistentCasingInFileNames": true
 
+    // "erasableSyntaxOnly": true
+
     /* Source Map Options */
     // "sourceRoot": "",                      /* Specify the location where debugger should locate TypeScript files instead of source locations. */
     // "mapRoot": "",                         /* Specify the location where debugger should locate map files instead of generated locations. */