diff --git a/.prettierrc b/.prettierrc
new file mode 100644
index 000000000..760df44e3
--- /dev/null
+++ b/.prettierrc
@@ -0,0 +1,6 @@
+{
+  "arrowParens": "always",
+  "semi": false,
+  "singleQuote": true,
+  "trailingComma": "all"
+}
diff --git a/package.json b/package.json
index e6e1b20ee..ec3ea5d4f 100644
--- a/package.json
+++ b/package.json
@@ -46,8 +46,9 @@
     "bundlesize": "0.17.0",
     "fetch-cookie": "0.7.2",
     "fetch-mock": "5.13.1",
-    "tslint": "5.9.1",
-    "tslint-config-standard": "7.0.0",
-    "typescript": "2.7.2"
+    "prettier": "1.14.2",
+    "tslint": "5.11.0",
+    "tslint-config-standard": "8.0.1",
+    "typescript": "3.0.3"
   }
 }
diff --git a/src/index.ts b/src/index.ts
index fa680707b..a3197981b 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,20 +1,28 @@
-import { ClientError, GraphQLError, Headers as HttpHeaders, Options, Variables } from './types'
-export { ClientError } from './types'
 import 'cross-fetch/polyfill'
 
+import { ClientError, GraphQLError, Variables } from './types'
+
+export { ClientError } from './types'
+
 export class GraphQLClient {
   private url: string
-  private options: Options
+  private options: RequestInit
 
-  constructor(url: string, options?: Options) {
+  constructor(url: string, options?: RequestInit) {
     this.url = url
     this.options = options || {}
   }
 
-  async rawRequest<T extends any>(
+  async rawRequest<T = any>(
     query: string,
     variables?: Variables,
-  ): Promise<{ data?: T, extensions?: any, headers: Headers, status: number, errors?: GraphQLError[] }> {
+  ): Promise<{
+    data?: T
+    extensions?: any
+    headers: Request['headers']
+    status: number
+    errors?: GraphQLError[]
+  }> {
     const { headers, ...others } = this.options
 
     const body = JSON.stringify({
@@ -24,7 +32,7 @@ export class GraphQLClient {
 
     const response = await fetch(this.url, {
       method: 'POST',
-      headers: Object.assign({ 'Content-Type': 'application/json' }, headers),
+      headers: { 'Content-Type': 'application/json', ...headers },
       body,
       ...others,
     })
@@ -44,10 +52,7 @@ export class GraphQLClient {
     }
   }
 
-  async request<T extends any>(
-    query: string,
-    variables?: Variables,
-  ): Promise<T> {
+  async request<T = any>(query: string, variables?: Variables): Promise<T> {
     const { headers, ...others } = this.options
 
     const body = JSON.stringify({
@@ -57,7 +62,7 @@ export class GraphQLClient {
 
     const response = await fetch(this.url, {
       method: 'POST',
-      headers: Object.assign({ 'Content-Type': 'application/json' }, headers),
+      headers: { 'Content-Type': 'application/json', ...headers },
       body,
       ...others,
     })
@@ -76,7 +81,7 @@ export class GraphQLClient {
     }
   }
 
-  setHeaders(headers: HttpHeaders): GraphQLClient {
+  setHeaders(headers: Response['headers']): GraphQLClient {
     this.options.headers = headers
 
     return this
@@ -94,17 +99,23 @@ export class GraphQLClient {
   }
 }
 
-export async function rawRequest<T extends any>(
+export async function rawRequest<T = any>(
   url: string,
   query: string,
   variables?: Variables,
-): Promise<{ data?: T, extensions?: any, headers: Headers, status: number, errors?: GraphQLError[] }> {
+): Promise<{
+  data?: T
+  extensions?: any
+  headers: Request['headers']
+  status: number
+  errors?: GraphQLError[]
+}> {
   const client = new GraphQLClient(url)
 
   return client.rawRequest<T>(query, variables)
 }
 
-export async function request<T extends any>(
+export async function request<T = any>(
   url: string,
   query: string,
   variables?: Variables,
diff --git a/src/types.ts b/src/types.ts
index e982f6458..9ab9e3dae 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -1,24 +1,8 @@
 export type Variables = { [key: string]: any }
 
-export interface Headers {
-  [key: string]: string
-}
-
-export interface Options {
-  method?: RequestInit['method']
-  headers?: Headers
-  mode?: RequestInit['mode']
-  credentials?: RequestInit['credentials']
-  cache?: RequestInit['cache']
-  redirect?: RequestInit['redirect']
-  referrer?: RequestInit['referrer']
-  referrerPolicy?: RequestInit['referrerPolicy']
-  integrity?: RequestInit['integrity']
-}
-
 export interface GraphQLError {
   message: string
-  locations: { line: number, column: number }[]
+  locations: { line: number; column: number }[]
   path: string[]
 }
 
@@ -36,12 +20,14 @@ export interface GraphQLRequestContext {
 }
 
 export class ClientError extends Error {
-
   response: GraphQLResponse
   request: GraphQLRequestContext
 
-  constructor (response: GraphQLResponse, request: GraphQLRequestContext) {
-    const message = `${ClientError.extractMessage(response)}: ${JSON.stringify({ response, request })}`
+  constructor(response: GraphQLResponse, request: GraphQLRequestContext) {
+    const message = `${ClientError.extractMessage(response)}: ${JSON.stringify({
+      response,
+      request,
+    })}`
 
     super(message)
 
@@ -55,7 +41,7 @@ export class ClientError extends Error {
     }
   }
 
-  private static extractMessage (response: GraphQLResponse): string {
+  private static extractMessage(response: GraphQLResponse): string {
     try {
       return response.errors![0].message
     } catch (e) {
diff --git a/tests/index.test.ts b/tests/index.test.ts
index 851064c01..a3194f8d2 100644
--- a/tests/index.test.ts
+++ b/tests/index.test.ts
@@ -1,7 +1,7 @@
 import test from 'ava'
 import * as fetchMock from 'fetch-mock'
+
 import { ClientError, rawRequest, request, GraphQLClient } from '../src/index'
-import { Options } from '../src/types'
 
 test('minimal query', async (t) => {
   const data = {
@@ -10,8 +10,11 @@ test('minimal query', async (t) => {
     },
   }
 
-  await mock({body: {data}}, async () => {
-    t.deepEqual(await request('https://mock-api.com/graphql', `{ viewer { id } }`), data)
+  await mock({ body: { data } }, async () => {
+    t.deepEqual(
+      await request('https://mock-api.com/graphql', `{ viewer { id } }`),
+      data,
+    )
   })
 })
 
@@ -26,9 +29,12 @@ test('minimal raw query', async (t) => {
     version: '1',
   }
 
-  await mock({body: {data, extensions}}, async () => {
-    const { headers, ...result } = await rawRequest('https://mock-api.com/graphql', `{ viewer { id } }`)
-    t.deepEqual(result, {data, extensions, status: 200})
+  await mock({ body: { data, extensions } }, async () => {
+    const { headers, ...result } = await rawRequest(
+      'https://mock-api.com/graphql',
+      `{ viewer { id } }`,
+    )
+    t.deepEqual(result, { data, extensions, status: 200 })
   })
 })
 
@@ -48,43 +54,53 @@ test('minimal raw query with response headers', async (t) => {
     'X-Custom-Header': 'test-custom-header',
   }
 
-  await mock({headers: reqHeaders, body: {data, extensions}}, async () => {
-    const { headers, ...result } = await rawRequest('https://mock-api.com/graphql', `{ viewer { id } }`)
-    t.deepEqual(result, {data, extensions, status: 200})
+  await mock({ headers: reqHeaders, body: { data, extensions } }, async () => {
+    const { headers, ...result } = await rawRequest(
+      'https://mock-api.com/graphql',
+      `{ viewer { id } }`,
+    )
+
+    t.deepEqual(result, { data, extensions, status: 200 })
     t.deepEqual(headers.get('X-Custom-Header'), reqHeaders['X-Custom-Header'])
   })
 })
 
 test('basic error', async (t) => {
   const errors = {
-    message: "Syntax Error GraphQL request (1:1) Unexpected Name \"x\"\n\n1: x\n   ^\n",
+    message:
+      'Syntax Error GraphQL request (1:1) Unexpected Name "x"\n\n1: x\n   ^\n',
     locations: [
       {
         line: 1,
-        column: 1
-      }
-    ]
+        column: 1,
+      },
+    ],
   }
 
-  await mock({body: {errors}}, async () => {
-    const err: ClientError = await t.throws(request('https://mock-api.com/graphql', `x`))
+  await mock({ body: { errors } }, async () => {
+    const err: ClientError = await t.throws(
+      request('https://mock-api.com/graphql', `x`),
+    )
     t.deepEqual<any>(err.response.errors, errors)
   })
 })
 
 test('raw request error', async (t) => {
   const errors = {
-    message: "Syntax Error GraphQL request (1:1) Unexpected Name \"x\"\n\n1: x\n   ^\n",
+    message:
+      'Syntax Error GraphQL request (1:1) Unexpected Name "x"\n\n1: x\n   ^\n',
     locations: [
       {
         line: 1,
-        column: 1
-      }
-    ]
+        column: 1,
+      },
+    ],
   }
 
-  await mock({body: {errors}}, async () => {
-    const err: ClientError = await t.throws(rawRequest('https://mock-api.com/graphql', `x`))
+  await mock({ body: { errors } }, async () => {
+    const err: ClientError = await t.throws(
+      rawRequest('https://mock-api.com/graphql', `x`),
+    )
     t.deepEqual<any>(err.response.errors, errors)
   })
 })
@@ -96,32 +112,40 @@ test('content-type with charset', async (t) => {
     },
   }
 
-  await mock({
-    headers: {'Content-Type': 'application/json; charset=utf-8'},
-    body: {data}
-  }, async () => {
-    t.deepEqual(await request('https://mock-api.com/graphql', `{ viewer { id } }`), data)
-  })
+  await mock(
+    {
+      headers: { 'Content-Type': 'application/json; charset=utf-8' },
+      body: { data },
+    },
+    async () => {
+      t.deepEqual(
+        await request('https://mock-api.com/graphql', `{ viewer { id } }`),
+        data,
+      )
+    },
+  )
 })
 
-
 test('extra fetch options', async (t) => {
-  const options: Options = {
+  const options: RequestInit = {
     credentials: 'include',
     mode: 'cors',
     cache: 'reload',
   }
 
   const client = new GraphQLClient('https://mock-api.com/graphql', options)
-  await mock({
-    body: { data: {test: 'test'} }
-  }, async () => {
-    await client.request('{ test }')
-    const actualOptions = fetchMock.lastCall()[1]
-    for (let name in options) {
-      t.deepEqual(actualOptions[name], options[name])
-    }
-  })
+  await mock(
+    {
+      body: { data: { test: 'test' } },
+    },
+    async () => {
+      await client.request('{ test }')
+      const actualOptions = fetchMock.lastCall()[1]
+      for (let name in options) {
+        t.deepEqual(actualOptions[name], options[name])
+      }
+    },
+  )
 })
 
 async function mock(response: any, testFn: () => Promise<void>) {
diff --git a/tsconfig.json b/tsconfig.json
index 0957ff49f..9ae4d965a 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,16 +1,14 @@
 {
   "compilerOptions": {
+    "lib": ["es2015", "es2016", "dom", "esnext.asynciterable"],
     "module": "commonjs",
     "moduleResolution": "node",
+    "noUnusedLocals": true,
+    "outDir": "dist",
     "rootDir": ".",
-    "target": "es5",
     "sourceMap": true,
     "strictNullChecks": true,
-    "noUnusedLocals": true,
-    "outDir": "dist",
-    "lib": ["es2015", "es2016", "dom", "esnext.asynciterable"]
+    "target": "es5"
   },
-  "exclude": [
-    "node_modules"
-  ]
+  "exclude": ["node_modules"]
 }
diff --git a/yarn.lock b/yarn.lock
index b755d58c3..b8694e1a5 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1127,7 +1127,7 @@ diff@^3.2.0:
   version "3.2.0"
   resolved "https://registry.yarnpkg.com/diff/-/diff-3.2.0.tgz#c9ce393a4b7cbd0b058a725c93df299027868ff9"
 
-doctrine@^0.7.2:
+doctrine@0.7.2:
   version "0.7.2"
   resolved "https://registry.yarnpkg.com/doctrine/-/doctrine-0.7.2.tgz#7cb860359ba3be90e040b26b729ce4bfa654c523"
   dependencies:
@@ -2553,6 +2553,10 @@ preserve@^0.2.0:
   version "0.2.0"
   resolved "https://registry.yarnpkg.com/preserve/-/preserve-0.2.0.tgz#815ed1f6ebc65926f865b310c0713bcb3315ce4b"
 
+prettier@1.14.2:
+  version "1.14.2"
+  resolved "https://registry.yarnpkg.com/prettier/-/prettier-1.14.2.tgz#0ac1c6e1a90baa22a62925f41963c841983282f9"
+
 pretty-ms@^0.2.1:
   version "0.2.2"
   resolved "https://registry.yarnpkg.com/pretty-ms/-/pretty-ms-0.2.2.tgz#da879a682ff33a37011046f13d627f67c73b84f6"
@@ -3222,31 +3226,35 @@ trim-right@^1.0.1:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/trim-right/-/trim-right-1.0.1.tgz#cb2e1203067e0c8de1f614094b9fe45704ea6003"
 
-tslib@^1.0.0:
-  version "1.7.1"
-  resolved "https://registry.yarnpkg.com/tslib/-/tslib-1.7.1.tgz#bc8004164691923a79fe8378bbeb3da2017538ec"
+tslib@1.9.0:
+  version "1.9.0"
+  resolved "https://registry.yarnpkg.com/tslib/-/tslib-1.9.0.tgz#e37a86fda8cbbaf23a057f473c9f4dc64e5fc2e8"
 
 tslib@^1.8.0:
   version "1.8.1"
   resolved "https://registry.yarnpkg.com/tslib/-/tslib-1.8.1.tgz#6946af2d1d651a7b1863b531d6e5afa41aa44eac"
 
-tslint-config-standard@7.0.0:
-  version "7.0.0"
-  resolved "https://registry.yarnpkg.com/tslint-config-standard/-/tslint-config-standard-7.0.0.tgz#47bbf25578ed2212456f892d51e1abe884a29f15"
+tslib@^1.8.1:
+  version "1.9.3"
+  resolved "https://registry.yarnpkg.com/tslib/-/tslib-1.9.3.tgz#d7e4dd79245d85428c4d7e4822a79917954ca286"
+
+tslint-config-standard@8.0.1:
+  version "8.0.1"
+  resolved "https://registry.yarnpkg.com/tslint-config-standard/-/tslint-config-standard-8.0.1.tgz#e4dd3128e84b0e34b51990b68715a641f2b417e4"
   dependencies:
-    tslint-eslint-rules "^4.1.1"
+    tslint-eslint-rules "^5.3.1"
 
-tslint-eslint-rules@^4.1.1:
-  version "4.1.1"
-  resolved "https://registry.yarnpkg.com/tslint-eslint-rules/-/tslint-eslint-rules-4.1.1.tgz#7c30e7882f26bc276bff91d2384975c69daf88ba"
+tslint-eslint-rules@^5.3.1:
+  version "5.4.0"
+  resolved "https://registry.yarnpkg.com/tslint-eslint-rules/-/tslint-eslint-rules-5.4.0.tgz#e488cc9181bf193fe5cd7bfca213a7695f1737b5"
   dependencies:
-    doctrine "^0.7.2"
-    tslib "^1.0.0"
-    tsutils "^1.4.0"
+    doctrine "0.7.2"
+    tslib "1.9.0"
+    tsutils "^3.0.0"
 
-tslint@5.9.1:
-  version "5.9.1"
-  resolved "https://registry.yarnpkg.com/tslint/-/tslint-5.9.1.tgz#1255f87a3ff57eb0b0e1f0e610a8b4748046c9ae"
+tslint@5.11.0:
+  version "5.11.0"
+  resolved "https://registry.yarnpkg.com/tslint/-/tslint-5.11.0.tgz#98f30c02eae3cde7006201e4c33cb08b48581eed"
   dependencies:
     babel-code-frame "^6.22.0"
     builtin-modules "^1.1.1"
@@ -3259,17 +3267,19 @@ tslint@5.9.1:
     resolve "^1.3.2"
     semver "^5.3.0"
     tslib "^1.8.0"
-    tsutils "^2.12.1"
+    tsutils "^2.27.2"
 
-tsutils@^1.4.0:
-  version "1.9.1"
-  resolved "https://registry.yarnpkg.com/tsutils/-/tsutils-1.9.1.tgz#b9f9ab44e55af9681831d5f28d0aeeaf5c750cb0"
+tsutils@^2.27.2:
+  version "2.29.0"
+  resolved "https://registry.yarnpkg.com/tsutils/-/tsutils-2.29.0.tgz#32b488501467acbedd4b85498673a0812aca0b99"
+  dependencies:
+    tslib "^1.8.1"
 
-tsutils@^2.12.1:
-  version "2.14.0"
-  resolved "https://registry.yarnpkg.com/tsutils/-/tsutils-2.14.0.tgz#bc5291622aa2448c1baffc544bcc14ecfa528fb7"
+tsutils@^3.0.0:
+  version "3.0.0"
+  resolved "https://registry.yarnpkg.com/tsutils/-/tsutils-3.0.0.tgz#0c5070a17a0503e056da038c48b5a1870a50a9ad"
   dependencies:
-    tslib "^1.8.0"
+    tslib "^1.8.1"
 
 tunnel-agent@^0.6.0:
   version "0.6.0"
@@ -3281,9 +3291,9 @@ tweetnacl@^0.14.3, tweetnacl@~0.14.0:
   version "0.14.5"
   resolved "https://registry.yarnpkg.com/tweetnacl/-/tweetnacl-0.14.5.tgz#5ae68177f192d4456269d108afa93ff8743f4f64"
 
-typescript@2.7.2:
-  version "2.7.2"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-2.7.2.tgz#2d615a1ef4aee4f574425cdff7026edf81919836"
+typescript@3.0.3:
+  version "3.0.3"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.0.3.tgz#4853b3e275ecdaa27f78fda46dc273a7eb7fc1c8"
 
 uid-number@^0.0.6:
   version "0.0.6"