diff --git a/.eslintrc.json b/.eslintrc.json
index a5b6f02..f85270a 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -14,7 +14,8 @@
   "extends": [
     "eslint:recommended",
     "plugin:eslint-comments/recommended",
-    "plugin:mocha/recommended"
+    "plugin:mocha/recommended",
+    "plugin:jsdoc/recommended-error"
   ],
   "globals": { "console": true },
   "rules": {
diff --git a/lib/index.js b/lib/index.js
index b5530db..04ff123 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -8,49 +8,43 @@ import mysql from "mysql";
  * @typedef {import('ioredis').Cluster} RedisCluster
  */
 
-function resolveEndpoint(shard) {
-  let portNum = 3306 - 1 + shard;
-  if (process.env[`DB_SHARD_${shard}_INTERNAL_PORT`]) {
-    portNum = parseInt(process.env[`DB_SHARD_${shard}_INTERNAL_PORT`] || "0");
+export class DB {
+  #pool;
+  resolveEndpoint(shard) {
+    let portNum = 3306 - 1 + shard;
+    if (process.env[`DB_SHARD_${shard}_INTERNAL_PORT`]) {
+      portNum = parseInt(process.env[`DB_SHARD_${shard}_INTERNAL_PORT`] || "0");
+    }
+    return {
+      host: process.env[`DB_SHARD_${shard}_INTERNAL_HOST`] || "127.0.0.1",
+      port: portNum,
+    };
   }
-  return {
-    host: process.env[`DB_SHARD_${shard}_INTERNAL_HOST`] || "127.0.0.1",
-    port: portNum,
-  };
-}
 
-/**
- * createPool.
- *
- * @param {number} shard
- * @returns {Promise<mysql.Pool>}
- */
-function createPool(shard) {
-  return new Promise((resolve, reject) => {
-    try {
-      const pool = mysql.createPool({
-        ...resolveEndpoint(shard),
-        user: `test_${shard}`,
-        password: "password",
-        database: `myproject_${shard}`,
-      });
-      resolve(pool);
-    } catch (e) {
-      reject(e);
-    }
-  });
-}
+  createPool(shard) {
+    return new Promise((resolve, reject) => {
+      try {
+        const pool = mysql.createPool({
+          ...this.resolveEndpoint(shard),
+          user: `test_${shard}`,
+          password: "password",
+          database: `myproject_${shard}`,
+        });
+        resolve(pool);
+      } catch (e) {
+        reject(e);
+      }
+    });
+  }
 
-export class DB {
-  #pool;
   constructor(shardNum = 1) {
-    this.#pool = createPool(shardNum);
+    this.#pool = this.createPool(shardNum);
   }
 
   /**
    * query.
-   * @param {string} sql
-   * @returns {Promise<[unknown, mysql.FieldInfo[]|undefined]>}
+   * @param {string} sql - sql
+   * @returns {Promise<[unknown, mysql.FieldInfo[]|undefined]>} - [results, fields]
    */
   async query(sql) {
     const pool = await this.#pool;
@@ -83,7 +77,6 @@ export class DB {
   }
 }
 
-//eslint-disable-next-line no-unused-vars
 class MEMConfig {
   /**
    * @type {string}
@@ -107,7 +100,7 @@ export class MEM {
   #conf;
   /**
    * constructor.
-   * @param {MEMConfig} [conf]
+   * @param {MEMConfig} [conf] - configuration
    */
   constructor(conf) {
     if (!conf) {
@@ -135,7 +128,7 @@ export class MEM {
 
   /**
    * connect.
-   * @returns {Promise<RedisCluster>}
+   * @returns {Promise<RedisCluster>} - redisio cluster
    */
   async connect() {
     const ports = [
diff --git a/package.json b/package.json
index fe7072d..b8adaf6 100644
--- a/package.json
+++ b/package.json
@@ -6,7 +6,8 @@
   "types": "./types/index.d.ts",
   "scripts": {
     "build": "tsc --declaration --emitDeclarationOnly --outDir types --allowJs --declarationMap lib/index.js",
-    "lint": "eslint --max-warnings=0 '{src,test}/**/*.{js,jsx}' && tsc --noEmit",
+    "lint": "eslint --max-warnings=0 '{lib,test}/**/*.{js,jsx}' && tsc --noEmit",
+    "lint:fix": "eslint --fix --max-warnings=0 '{lib,test}/**/*.{js,jsx}' && tsc --noEmit",
     "test": "mocha 'test/**/*.spec.{js,jsx}'",
     "test:watch": "npm run test -- --watch --watch-files src,test",
     "fmt:base": "prettier '{src,test}/**/*.{js,jsx}'",