diff --git a/README.md b/README.md
index 5a17ddc73..32fae0aa2 100644
--- a/README.md
+++ b/README.md
@@ -113,7 +113,7 @@ const { data, error, isValidating, mutate } = useSWR(key, fetcher, options)
 #### Options
 
 - `suspense = false`: enable React Suspense mode [(details)](#suspense-mode)
-- `fetcher = window.fetch`: the default fetcher function
+- `fetcher`: the function to retrieve the remote data source
 - `initialData`: initial data to be returned (note: This is per-hook)
 - `revalidateOnMount`: enable or disable automatic revalidation when component is mounted (by default revalidation occurs on mount when initialData is not set, use this flag to force behavior)
 - `revalidateOnFocus = true`: auto revalidate when window gets focused
diff --git a/src/types.ts b/src/types.ts
index d73fd1c39..31c5fdc89 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -18,7 +18,7 @@ export interface Configuration<
   shouldRetryOnError: boolean
   suspense?: boolean
   initialData?: Data
-  fetcher: Fn
+  fetcher?: Fn
   cache: Cache
   middlewares?: Middleware[]
 
diff --git a/src/utils/config.ts b/src/utils/config.ts
index 1a30c5445..4f4e44ee7 100644
--- a/src/utils/config.ts
+++ b/src/utils/config.ts
@@ -6,7 +6,6 @@ import { slowConnection } from './env'
 import { Configuration, RevalidatorOptions, Revalidator } from '../types'
 import { UNDEFINED } from './helper'
 
-const fetcher = (url: string) => fetch(url).then(res => res.json())
 const noop = () => {}
 
 // error retry
@@ -56,7 +55,6 @@ const defaultConfig: Configuration = {
   loadingTimeout: slowConnection ? 5000 : 3000,
 
   // providers
-  fetcher,
   compare: dequal,
   isPaused: () => false,
   cache: wrapCache(new Map()),
diff --git a/test/use-swr-integration.test.tsx b/test/use-swr-integration.test.tsx
index 585980d4e..c4d318610 100644
--- a/test/use-swr-integration.test.tsx
+++ b/test/use-swr-integration.test.tsx
@@ -357,27 +357,4 @@ describe('useSWR', () => {
     expect(fetcher).toBeCalled()
     await screen.findByText('hello, SWR')
   })
-
-  it('should use fetch api as default fetcher', async () => {
-    const users = [{ name: 'bob' }, { name: 'sue' }]
-    global['fetch'] = () => Promise.resolve()
-    const mockFetch = body =>
-      Promise.resolve({ json: () => Promise.resolve(body) } as any)
-    const fn = jest
-      .spyOn(window, 'fetch')
-      .mockImplementation(() => mockFetch(users))
-
-    function Users() {
-      const { data } = useSWR('http://localhost:3000/api/users')
-
-      return <div>hello, {data && data.map(u => u.name).join(' and ')}</div>
-    }
-
-    render(<Users />)
-    screen.getByText('hello,')
-    expect(fn).toBeCalled()
-
-    await screen.findByText('hello, bob and sue')
-    delete global['fetch']
-  })
 })
diff --git a/test/use-swr-local-mutation.test.tsx b/test/use-swr-local-mutation.test.tsx
index cec53f775..db0c70c1d 100644
--- a/test/use-swr-local-mutation.test.tsx
+++ b/test/use-swr-local-mutation.test.tsx
@@ -2,7 +2,7 @@ import { act, render, screen, fireEvent } from '@testing-library/react'
 import React, { useEffect, useState } from 'react'
 import useSWR, { mutate, createCache, SWRConfig } from 'swr'
 import { serialize } from '../src/utils/serialize'
-import { createResponse, sleep, nextTick as waitForNextTick } from './utils'
+import { createResponse, sleep, nextTick } from './utils'
 
 describe('useSWR - local mutation', () => {
   it('should trigger revalidation programmatically', async () => {
@@ -29,6 +29,33 @@ describe('useSWR - local mutation', () => {
     await screen.findByText('data: 1')
   })
 
+  it('should share local state when no fetcher is specified', async () => {
+    const useSharedState = (key, initialData) => {
+      const { data: state, mutate: setState } = useSWR(key, { initialData })
+      return [state, setState]
+    }
+
+    function Page() {
+      const [name, setName] = useSharedState('name', 'huozhi')
+      const [job, setJob] = useSharedState('job', 'gardener')
+
+      return (
+        <span
+          onClick={() => {
+            setName('@huozhi')
+            setJob('chef')
+          }}
+        >
+          {name}:{job}
+        </span>
+      )
+    }
+    render(<Page />)
+    const root = screen.getByText('huozhi:gardener')
+    fireEvent.click(root)
+    await screen.findByText('@huozhi:chef')
+  })
+
   it('should trigger revalidation programmatically within a dedupingInterval', async () => {
     let value = 0
 
@@ -144,7 +171,7 @@ describe('useSWR - local mutation', () => {
     //mount
     await screen.findByText('data: 0')
 
-    await waitForNextTick()
+    await nextTick()
     await act(() => {
       // mutate and revalidate
       return mutate('mutate-promise', createResponse(999), false)
@@ -167,7 +194,7 @@ describe('useSWR - local mutation', () => {
     //mount
     await screen.findByText('data: 0')
 
-    await waitForNextTick()
+    await nextTick()
     await act(() => {
       // mutate and revalidate
       return mutate('mutate-async-fn', async () => createResponse(999), false)