diff --git a/.gitignore b/.gitignore
index c90d1cc7b..d022dbedb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,6 +17,7 @@ coverage
 /plugin
 dayjs.min.js
 /esm
+index.d.ts
 
 #dev
 demo.js
diff --git a/.npmignore b/.npmignore
index 4f08223c0..1839a8b65 100644
--- a/.npmignore
+++ b/.npmignore
@@ -15,6 +15,7 @@ coverage
 # dev
 src
 test
+types
 build
 .babelrc
 .eslintrc.json
@@ -25,4 +26,4 @@ docs
 
 #other
 .travis.yml
-karma.sauce.conf.js
\ No newline at end of file
+karma.sauce.conf.js
diff --git a/build/index.js b/build/index.js
index a5e08fda6..0dd2e134b 100644
--- a/build/index.js
+++ b/build/index.js
@@ -3,6 +3,7 @@ const configFactory = require('./rollup.config')
 const fs = require('fs')
 const util = require('util')
 const path = require('path')
+const mergedirs = require('merge-dirs').default
 
 const { promisify } = util
 
@@ -39,6 +40,8 @@ async function build(option) {
       input: './src/index.js',
       fileName: './dayjs.min.js'
     }))
+
+    mergedirs('./types/', './', 'overwrite')
   } catch (e) {
     console.error(e) // eslint-disable-line no-console
   }
diff --git a/package.json b/package.json
index c600258e1..acdf3ba8a 100644
--- a/package.json
+++ b/package.json
@@ -6,7 +6,7 @@
   "types": "index.d.ts",
   "module": "dayjs.min.js",
   "scripts": {
-    "test": "TZ=Pacific/Auckland npm run test-tz && TZ=Europe/London npm run test-tz && npm run test-tz && jest",
+    "test": "TZ=Pacific/Auckland npm run test-tz && TZ=Europe/London npm run test-tz && npm run test-tz && tsc && jest",
     "test-tz": "jest test/timezone.test --coverage=false",
     "lint": "./node_modules/.bin/eslint src/* test/* build/*",
     "prettier": "prettier --write \"docs/**/*.md\"",
@@ -84,11 +84,12 @@
     "karma": "^2.0.2",
     "karma-jasmine": "^1.1.2",
     "karma-sauce-launcher": "^1.1.0",
+    "merge-dirs": "^0.2.1",
     "mockdate": "^2.0.2",
     "moment": "^2.22.0",
     "pre-commit": "^1.2.2",
     "prettier": "^1.16.1",
-    "rollup": "^0.57.1",
+    "rollup": "^0.67.3",
     "rollup-plugin-babel": "^4.0.0-beta.4",
     "rollup-plugin-uglify": "^3.0.0",
     "size-limit": "^0.18.0",
diff --git a/test/index.d.test.ts b/test/index.d.test.ts
index 4e6edb44c..ab800bab7 100644
--- a/test/index.d.test.ts
+++ b/test/index.d.test.ts
@@ -1,4 +1,4 @@
-import dayjs from '../src'
+import * as dayjs from 'dayjs'
 
 dayjs()
 
@@ -8,6 +8,12 @@ dayjs(730944000000)
 
 dayjs(new Date(1993, 3, 1))
 
+dayjs('05/02/69 1:02:03 PM -05:00', 'MM/DD/YY H:mm:ss A Z')
+
+dayjs('05/02/69 1:02:03 PM -05:00', { format: 'MM/DD/YY H:mm:ss A Z' })
+
+dayjs('1993-03-1', { locale: 'ja' })
+
 dayjs().clone()
 
 dayjs().isValid()
@@ -70,10 +76,16 @@ dayjs().isSame(dayjs())
 
 dayjs().isAfter(dayjs())
 
-dayjs().isBefore(dayjs(), 'minutes')
+dayjs().isBefore(dayjs(), 'minute')
 
-dayjs().isSame(dayjs(), 'hours')
+dayjs().isSame(dayjs(), 'hour')
 
 dayjs().isAfter(dayjs(), 'year')
 
 dayjs('2000-01-01').isLeapYear()
+
+dayjs.extend((o, c, d) => {
+  o.locale.trim()
+  new c().unix() // eslint-disable-line new-cap
+  d().unix()
+})
diff --git a/test/plugin/dayOfYear.d.test.ts b/test/plugin/dayOfYear.d.test.ts
new file mode 100644
index 000000000..85173c66e
--- /dev/null
+++ b/test/plugin/dayOfYear.d.test.ts
@@ -0,0 +1,6 @@
+import * as dayjs from 'dayjs'
+import * as dayOfYear from 'dayjs/plugin/dayOfYear'
+
+dayjs.extend(dayOfYear)
+
+dayjs('2015-01-01T00:00:00.000').dayOfYear() === 1
diff --git a/test/plugin/isBetween.d.test.ts b/test/plugin/isBetween.d.test.ts
new file mode 100644
index 000000000..4542e4b61
--- /dev/null
+++ b/test/plugin/isBetween.d.test.ts
@@ -0,0 +1,6 @@
+import * as dayjs from 'dayjs'
+import * as isBetween from 'dayjs/plugin/isBetween'
+
+dayjs.extend(isBetween)
+
+dayjs('2010-10-20').isBetween('2010-10-19', dayjs('2010-10-25')) === true
diff --git a/test/plugin/isLeapYear.d.test.ts b/test/plugin/isLeapYear.d.test.ts
new file mode 100644
index 000000000..399930658
--- /dev/null
+++ b/test/plugin/isLeapYear.d.test.ts
@@ -0,0 +1,6 @@
+import * as dayjs from 'dayjs'
+import * as isLeapYear from 'dayjs/plugin/isLeapYear'
+
+dayjs.extend(isLeapYear)
+
+dayjs('2010-10-20').isLeapYear() === false
diff --git a/test/plugin/isSameOrAfter.d.test.ts b/test/plugin/isSameOrAfter.d.test.ts
new file mode 100644
index 000000000..b8f257cfd
--- /dev/null
+++ b/test/plugin/isSameOrAfter.d.test.ts
@@ -0,0 +1,6 @@
+import * as dayjs from 'dayjs'
+import * as isSameOrAfter from 'dayjs/plugin/isSameOrAfter'
+
+dayjs.extend(isSameOrAfter)
+
+dayjs('2010-10-20').isSameOrAfter('2010-10-19', 'year') === true
diff --git a/test/plugin/isSameOrBefore.d.test.ts b/test/plugin/isSameOrBefore.d.test.ts
new file mode 100644
index 000000000..5dcf966ee
--- /dev/null
+++ b/test/plugin/isSameOrBefore.d.test.ts
@@ -0,0 +1,6 @@
+import * as dayjs from 'dayjs'
+import * as isSameOrBefore from 'dayjs/plugin/isSameOrBefore'
+
+dayjs.extend(isSameOrBefore)
+
+dayjs('2010-10-20').isSameOrBefore('2010-10-19', 'year') === true
diff --git a/test/plugin/quarterOfYear.d.test.ts b/test/plugin/quarterOfYear.d.test.ts
new file mode 100644
index 000000000..f3f2b8ae7
--- /dev/null
+++ b/test/plugin/quarterOfYear.d.test.ts
@@ -0,0 +1,6 @@
+import * as dayjs from 'dayjs'
+import * as quarterOfYear from 'dayjs/plugin/quarterOfYear'
+
+dayjs.extend(quarterOfYear)
+
+dayjs('2013-01-01T00:00:00.000').quarter() === 1
diff --git a/test/plugin/relativeTime.d.test.ts b/test/plugin/relativeTime.d.test.ts
new file mode 100644
index 000000000..1124553f0
--- /dev/null
+++ b/test/plugin/relativeTime.d.test.ts
@@ -0,0 +1,20 @@
+import * as dayjs from 'dayjs'
+import * as relativeTime from 'dayjs/plugin/relativeTime'
+
+dayjs.extend(relativeTime)
+
+dayjs().fromNow().trim()
+dayjs().fromNow(true).trim()
+
+dayjs().from(dayjs()).trim()
+dayjs().from(123, true).trim()
+dayjs().from('2018-01-23').trim()
+dayjs().from(new Date(), true).trim()
+
+dayjs().toNow().trim()
+dayjs().toNow(true).trim()
+
+dayjs().to(dayjs()).trim()
+dayjs().to(123, true).trim()
+dayjs().to('2018-01-23').trim()
+dayjs().to(new Date(), true).trim()
diff --git a/test/plugin/weekOfYear.d.test.ts b/test/plugin/weekOfYear.d.test.ts
new file mode 100644
index 000000000..bfaceede9
--- /dev/null
+++ b/test/plugin/weekOfYear.d.test.ts
@@ -0,0 +1,6 @@
+import * as dayjs from 'dayjs'
+import * as weekOfYear from 'dayjs/plugin/weekOfYear'
+
+dayjs.extend(weekOfYear)
+
+dayjs('2010-10-20').week() === 43
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 000000000..c79e47e21
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,20 @@
+{
+  "compilerOptions": {
+    "strict": true,
+    "noEmit": true,
+    "lib": [
+      // TODO: Unfortunately, rollup brings @types/node and etc. with "dependencies", not "devDependencies".
+      // It references Symbol type.
+      "es5",
+      "es2015.symbol"
+    ],
+    "baseUrl": "./types",
+    "paths": {
+      "dayjs": [ "." ],
+      "dayjs/*": [ "*" ]
+    }
+  },
+  "exclude": [
+    "node_modules"
+  ]
+}
diff --git a/index.d.ts b/types/index.d.ts
similarity index 58%
rename from index.d.ts
rename to types/index.d.ts
index 236a7d274..e1733a902 100644
--- a/index.d.ts
+++ b/types/index.d.ts
@@ -1,10 +1,13 @@
 export = dayjs;
-declare function dayjs (config?: dayjs.ConfigType, option?: dayjs.OptionType): dayjs.Dayjs
+declare function dayjs (date?: dayjs.DateType, option?: dayjs.OptionType): dayjs.Dayjs
 
 declare namespace dayjs {
-  export type ConfigType = string | number | Date | Dayjs
+  export type DateType = string | number | Date | Dayjs
 
-  export type OptionType = { locale: string }
+  /** @deprecated Renamed to DateType. */
+  export type ConfigType = DateType
+
+  export type OptionType = { locale?: string, format?: string } | string
 
   type UnitTypeShort = 'd' | 'M' | 'y' | 'h' | 'm' | 's' | 'ms'
   export type UnitType = 'millisecond' | 'second' | 'minute' | 'hour' | 'day' | 'month' | 'quarter' | 'year' | 'date' | UnitTypeShort;
@@ -23,7 +26,7 @@ declare namespace dayjs {
   }
 
   class Dayjs {
-    constructor (config?: ConfigType)
+    constructor (date?: DateType)
 
     clone(): Dayjs
 
@@ -57,7 +60,7 @@ declare namespace dayjs {
 
     format(template?: string): string
 
-    diff(dayjs: ConfigType, unit: OpUnitType, float?: boolean): number
+    diff(date: DateType, unit: OpUnitType, float?: boolean): number
 
     valueOf(): number
 
@@ -77,24 +80,24 @@ declare namespace dayjs {
 
     toString(): string
 
-    isBefore(dayjs: ConfigType, unit?: OpUnitType): boolean
+    isBefore(date: DateType, unit?: OpUnitType): boolean
 
-    isSame(dayjs: ConfigType, unit?: OpUnitType): boolean
+    isSame(date: DateType, unit?: OpUnitType): boolean
 
-    isAfter(dayjs: ConfigType, unit?: OpUnitType): boolean
+    isAfter(date: DateType, unit?: OpUnitType): boolean
 
     isLeapYear(): boolean
 
-    locale(arg1: any, arg2?: any): Dayjs
+    locale(preset: string | { name: string, [key: string]: any }, object?: { [key: string]: any }): Dayjs
   }
 
-  export type PluginFunc = (option: ConfigType, d1: Dayjs, d2: Dayjs) => void
+  export type PluginFunc = (option: any, c: typeof Dayjs, d: typeof dayjs) => void
 
-  export function extend(plugin: PluginFunc, option?: ConfigType): Dayjs
+  export function extend(plugin: PluginFunc, option?: any): Dayjs
 
-  export function locale(arg1: any, arg2?: any): string
+  export function locale(preset: string | { name: string, [key: string]: any }, object?: { [key: string]: any }, isLocal?: boolean): string
 
   export function isDayjs(d: any): d is Dayjs
-  
+
   export function unix(t: number): Dayjs
 }
diff --git a/types/plugin/advancedFormat.d.ts b/types/plugin/advancedFormat.d.ts
new file mode 100644
index 000000000..30ec75e5d
--- /dev/null
+++ b/types/plugin/advancedFormat.d.ts
@@ -0,0 +1,4 @@
+import { PluginFunc } from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin
diff --git a/types/plugin/buddhistEra.d.ts b/types/plugin/buddhistEra.d.ts
new file mode 100644
index 000000000..30ec75e5d
--- /dev/null
+++ b/types/plugin/buddhistEra.d.ts
@@ -0,0 +1,4 @@
+import { PluginFunc } from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin
diff --git a/types/plugin/customParseFormat.ts b/types/plugin/customParseFormat.ts
new file mode 100644
index 000000000..30ec75e5d
--- /dev/null
+++ b/types/plugin/customParseFormat.ts
@@ -0,0 +1,4 @@
+import { PluginFunc } from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin
diff --git a/types/plugin/dayOfYear.d.ts b/types/plugin/dayOfYear.d.ts
new file mode 100644
index 000000000..028385152
--- /dev/null
+++ b/types/plugin/dayOfYear.d.ts
@@ -0,0 +1,10 @@
+import { PluginFunc } from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin
+
+declare module 'dayjs' {
+  interface Dayjs {
+    dayOfYear(): number
+  }
+}
diff --git a/types/plugin/isBetween.d.ts b/types/plugin/isBetween.d.ts
new file mode 100644
index 000000000..41afb64cf
--- /dev/null
+++ b/types/plugin/isBetween.d.ts
@@ -0,0 +1,10 @@
+import { PluginFunc, DateType } from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin
+
+declare module 'dayjs' {
+  interface Dayjs {
+    isBetween(a: DateType, b: DateType): boolean
+  }
+}
diff --git a/types/plugin/isLeapYear.d.ts b/types/plugin/isLeapYear.d.ts
new file mode 100644
index 000000000..5be74092b
--- /dev/null
+++ b/types/plugin/isLeapYear.d.ts
@@ -0,0 +1,10 @@
+import { PluginFunc } from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin
+
+declare module 'dayjs' {
+  interface Dayjs {
+    isLeapYear(): boolean
+  }
+}
diff --git a/types/plugin/isSameOrAfter.d.ts b/types/plugin/isSameOrAfter.d.ts
new file mode 100644
index 000000000..12d6f889d
--- /dev/null
+++ b/types/plugin/isSameOrAfter.d.ts
@@ -0,0 +1,10 @@
+import { PluginFunc } from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin
+
+declare module 'dayjs' {
+  interface Dayjs {
+    isSameOrAfter(date: DateType, unit?: OpUnitType): boolean
+  }
+}
diff --git a/types/plugin/isSameOrBefore.d.ts b/types/plugin/isSameOrBefore.d.ts
new file mode 100644
index 000000000..3442c69ad
--- /dev/null
+++ b/types/plugin/isSameOrBefore.d.ts
@@ -0,0 +1,10 @@
+import { PluginFunc } from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin
+
+declare module 'dayjs' {
+  interface Dayjs {
+    isSameOrBefore(date: DateType, unit?: OpUnitType): boolean
+  }
+}
diff --git a/types/plugin/localizedFormat.d.ts b/types/plugin/localizedFormat.d.ts
new file mode 100644
index 000000000..30ec75e5d
--- /dev/null
+++ b/types/plugin/localizedFormat.d.ts
@@ -0,0 +1,4 @@
+import { PluginFunc } from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin
diff --git a/types/plugin/quarterOfYear.d.ts b/types/plugin/quarterOfYear.d.ts
new file mode 100644
index 000000000..e8aad14b8
--- /dev/null
+++ b/types/plugin/quarterOfYear.d.ts
@@ -0,0 +1,10 @@
+import { PluginFunc } from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin
+
+declare module 'dayjs' {
+  interface Dayjs {
+    quarter(): number
+  }
+}
diff --git a/types/plugin/relativeTime.d.ts b/types/plugin/relativeTime.d.ts
new file mode 100644
index 000000000..306493002
--- /dev/null
+++ b/types/plugin/relativeTime.d.ts
@@ -0,0 +1,13 @@
+import { PluginFunc, DateType } from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin
+
+declare module 'dayjs' {
+  interface Dayjs {
+    fromNow(withoutSuffix?: boolean): string
+    from(compared: DateType, withoutSuffix?: boolean): string
+    toNow(withoutSuffix?: boolean): string
+    to(compared: DateType, withoutSuffix?: boolean): string
+  }
+}
diff --git a/types/plugin/weekOfYear.d.ts b/types/plugin/weekOfYear.d.ts
new file mode 100644
index 000000000..360219556
--- /dev/null
+++ b/types/plugin/weekOfYear.d.ts
@@ -0,0 +1,10 @@
+import { PluginFunc } from 'dayjs'
+
+declare const plugin: PluginFunc
+export = plugin
+
+declare module 'dayjs' {
+  interface Dayjs {
+    week(): number
+  }
+}