diff --git a/lib/config/index.ts b/lib/config/index.ts
index 3e4339363..8e8a91685 100644
--- a/lib/config/index.ts
+++ b/lib/config/index.ts
@@ -2,10 +2,17 @@ import crypto from 'crypto'
 import fs from 'fs'
 import path from 'path'
 import { merge } from 'lodash'
-import deepFreeze = require('deep-freeze')
 import { Environment, Permission } from './enum'
 import { logger } from '../logger'
 import { getGitCommit, getGitHubURL } from './utils'
+import { defaultConfig } from './default'
+import { defaultSSL } from './defaultSSL'
+import { oldDefault } from './oldDefault'
+import { oldEnvironment } from './oldEnvironment'
+import { hackmdEnvironment } from './hackmdEnvironment'
+import { environment } from './environment'
+import { dockerSecret } from './dockerSecret'
+import deepFreeze = require('deep-freeze')
 
 const appRootPath = path.resolve(__dirname, '../../')
 const env = process.env.NODE_ENV || Environment.development
@@ -28,19 +35,17 @@ const packageConfig = {
 }
 
 const configFilePath = path.resolve(appRootPath, process.env.CMD_CONFIG_FILE ||
-'config.json')
+  'config.json')
 const fileConfig = fs.existsSync(configFilePath) ? require(configFilePath)[env] : undefined
-
-let defaultConfig = require('./default')
-merge(defaultConfig, require('./defaultSSL'))
-merge(defaultConfig, require('./oldDefault'))
+merge(defaultConfig, defaultSSL)
+merge(defaultConfig, oldDefault)
 merge(defaultConfig, debugConfig)
 merge(defaultConfig, packageConfig)
 merge(defaultConfig, fileConfig)
-merge(defaultConfig, require('./oldEnvironment'))
-merge(defaultConfig, require('./hackmdEnvironment'))
-merge(defaultConfig, require('./environment'))
-merge(defaultConfig, require('./dockerSecret'))
+merge(defaultConfig, oldEnvironment)
+merge(defaultConfig, hackmdEnvironment)
+merge(defaultConfig, environment)
+merge(defaultConfig, dockerSecret)
 
 if (['debug', 'verbose', 'info', 'warn', 'error'].includes(defaultConfig.loglevel)) {
   logger.level = defaultConfig.loglevel
@@ -49,15 +54,15 @@ if (['debug', 'verbose', 'info', 'warn', 'error'].includes(defaultConfig.logleve
 }
 
 // load LDAP CA
-if (defaultConfig.ldap.tlsca) {
-  let ca = defaultConfig.ldap.tlsca.split(',')
-  let caContent: string[] = []
-  for (let i of ca) {
+if (defaultConfig.ldap?.tlsca) {
+  const ca = defaultConfig.ldap.tlsca.split(',')
+  const caContent: string[] = []
+  for (const i of ca) {
     if (fs.existsSync(i)) {
       caContent.push(fs.readFileSync(i, 'utf8'))
     }
   }
-  let tlsOptions = {
+  const tlsOptions = {
     ca: caContent
   }
   defaultConfig.ldap.tlsOptions = defaultConfig.ldap.tlsOptions ? Object.assign(defaultConfig.ldap.tlsOptions, tlsOptions) : tlsOptions
@@ -73,18 +78,18 @@ if (!(defaultConfig.defaultPermission in defaultConfig.permission)) {
 }
 
 // cache result, cannot change config in runtime!!!
-defaultConfig.isStandardHTTPsPort = (function isStandardHTTPsPort () {
+defaultConfig.isStandardHTTPsPort = (function isStandardHTTPsPort (): boolean {
   return defaultConfig.useSSL && defaultConfig.port === 443
 })()
-defaultConfig.isStandardHTTPPort = (function isStandardHTTPPort () {
+defaultConfig.isStandardHTTPPort = (function isStandardHTTPPort (): boolean {
   return !defaultConfig.useSSL && defaultConfig.port === 80
 })()
 
 // cache serverURL
-defaultConfig.serverURL = (function getserverurl () {
-  var url = ''
+defaultConfig.serverURL = (function getserverurl (): string {
+  let url = ''
   if (defaultConfig.domain) {
-    var protocol = defaultConfig.protocolUseSSL ? 'https://' : 'http://'
+    const protocol = defaultConfig.protocolUseSSL ? 'https://' : 'http://'
     url = protocol + defaultConfig.domain
     if (defaultConfig.urlAddPort) {
       if (!defaultConfig.isStandardHTTPPort || !defaultConfig.isStandardHTTPsPort) {
@@ -105,17 +110,17 @@ if (defaultConfig.serverURL === '') {
 defaultConfig.Environment = Environment
 
 // auth method
-defaultConfig.isFacebookEnable = defaultConfig.facebook.clientID && defaultConfig.facebook.clientSecret
-defaultConfig.isGoogleEnable = defaultConfig.google.clientID && defaultConfig.google.clientSecret
-defaultConfig.isDropboxEnable = defaultConfig.dropbox.clientID && defaultConfig.dropbox.clientSecret
-defaultConfig.isTwitterEnable = defaultConfig.twitter.consumerKey && defaultConfig.twitter.consumerSecret
+defaultConfig.isFacebookEnable = defaultConfig.facebook?.clientID && defaultConfig.facebook.clientSecret
+defaultConfig.isGoogleEnable = defaultConfig.google?.clientID && defaultConfig.google.clientSecret
+defaultConfig.isDropboxEnable = defaultConfig.dropbox?.clientID && defaultConfig.dropbox.clientSecret
+defaultConfig.isTwitterEnable = defaultConfig.twitter?.consumerKey && defaultConfig.twitter.consumerSecret
 defaultConfig.isEmailEnable = defaultConfig.email
 defaultConfig.isOpenIDEnable = defaultConfig.openID
-defaultConfig.isGitHubEnable = defaultConfig.github.clientID && defaultConfig.github.clientSecret
-defaultConfig.isGitLabEnable = defaultConfig.gitlab.clientID && defaultConfig.gitlab.clientSecret
-defaultConfig.isLDAPEnable = defaultConfig.ldap.url
-defaultConfig.isSAMLEnable = defaultConfig.saml.idpSsoUrl
-defaultConfig.isOAuth2Enable = defaultConfig.oauth2.clientID && defaultConfig.oauth2.clientSecret
+defaultConfig.isGitHubEnable = defaultConfig.github?.clientID && defaultConfig.github.clientSecret
+defaultConfig.isGitLabEnable = defaultConfig.gitlab?.clientID && defaultConfig.gitlab.clientSecret
+defaultConfig.isLDAPEnable = defaultConfig.ldap?.url
+defaultConfig.isSAMLEnable = defaultConfig.saml?.idpSsoUrl
+defaultConfig.isOAuth2Enable = defaultConfig.oauth2?.clientID && defaultConfig.oauth2.clientSecret
 
 // Check gitlab api version
 if (defaultConfig.gitlab && defaultConfig.gitlab.version !== 'v4' && defaultConfig.gitlab.version !== 'v3') {
@@ -123,30 +128,30 @@ if (defaultConfig.gitlab && defaultConfig.gitlab.version !== 'v4' && defaultConf
   defaultConfig.gitlab.version = 'v4'
 }
 // If gitlab scope is api, enable snippets Export/import
-defaultConfig.isGitlabSnippetsEnable = (!defaultConfig.gitlab.scope || defaultConfig.gitlab.scope === 'api') && defaultConfig.isGitLabEnable
+defaultConfig.isGitlabSnippetsEnable = (!defaultConfig.gitlab?.scope || defaultConfig.gitlab.scope === 'api') && defaultConfig.isGitLabEnable
 
 // Only update i18n files in development setups
 defaultConfig.updateI18nFiles = (env === Environment.development)
 
 // merge legacy values
-let keys = Object.keys(defaultConfig)
+const keys = Object.keys(defaultConfig)
 const uppercase = /[A-Z]/
 for (let i = keys.length; i--;) {
-  let lowercaseKey = keys[i].toLowerCase()
+  const lowercaseKey = keys[i].toLowerCase()
   // if the config contains uppercase letters
   // and a lowercase version of this setting exists
   // and the config with uppercase is not set
   // we set the new config using the old key.
   if (uppercase.test(keys[i]) &&
-  defaultConfig[lowercaseKey] !== undefined &&
-  fileConfig[keys[i]] === undefined) {
+    defaultConfig[lowercaseKey] !== undefined &&
+    fileConfig[keys[i]] === undefined) {
     logger.warn('config.js contains deprecated lowercase setting for ' + keys[i] + '. Please change your config.js file to replace ' + lowercaseKey + ' with ' + keys[i])
     defaultConfig[keys[i]] = defaultConfig[lowercaseKey]
   }
 }
 
 // Notify users about the prefix change and inform them they use legacy prefix for environment variables
-if (Object.keys(process.env).toString().indexOf('HMD_') !== -1) {
+if (Object.keys(process.env).toString().includes('HMD_')) {
   logger.warn('Using legacy HMD prefix for environment variables. Please change your variables in future. For details see: https://github.com/codimd/server#environment-variables-will-overwrite-other-server-configs')
 }
 
@@ -159,7 +164,7 @@ if (defaultConfig.sessionSecret === 'secret') {
 }
 
 // Validate upload upload providers
-if (['filesystem', 's3', 'minio', 'imgur', 'azure', 'lutim'].indexOf(defaultConfig.imageUploadType) === -1) {
+if (!['filesystem', 's3', 'minio', 'imgur', 'azure', 'lutim'].includes(defaultConfig.imageUploadType)) {
   logger.error('"imageuploadtype" is not correctly set. Please use "filesystem", "s3", "minio", "azure", "lutim" or "imgur". Defaulting to "filesystem"')
   defaultConfig.imageUploadType = 'filesystem'
 }