Fix ReqBase<TData>['error'] type (#334)

* Fix ReqBase<TData>['error'] type

It is currently marked as always having a value. But this is not true, its value is `undefined` when the request is either loading or successful. 

This means that checking whether the `error` property has a value will trigger `@typescript-eslint/strict-boolean-expressions`

ESLint rule doc: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/strict-boolean-expressions.md

Example playground: https://www.typescriptlang.org/play?#code/JYWwDg9gTgLgBAVwM4FMBiKYGMAWcBmUEIcA5MigLQ4wxikBQDWEAdkvAN5wA2EAhgBNgrAOYAaOCihEokwfxj84AXzgBeRKgzYcAClI06SAFwB6MygAe-cDxQA6FiDP8wwUpM4rJAbQC6AJRMwPhwetKygXCcDHDxcCzsEPYOfKIGACo4KHAwAJ5gKEhwSPz5eTjAJUnCMMBscADuwDw8cPw8TeUlAEa5MFAIKKTBKgxAA

* Fix ArrayDestructure types in useMutation and useQuery.

* Update tests.

Co-authored-by: Zebulan Stanphill <zebulanstanphill@protonmail.com>

Author: alexburner

src/__tests__/useFetch.test.tsx

@@ -168,7 +168,7 @@ describe('useFetch - responseType', (): void => {
     expect(result.current.loading).toBe(true)
     await waitForNextUpdate()
     expect(result.current.loading).toBe(false)
-    expect(result.current.error.name).toBe('FetchError')
+    expect(result.current.error?.name).toBe('FetchError')
   })
 
   it('should process .text() with default array responseType', async (): Promise<void> => {
@@ -353,8 +353,8 @@ describe('timeouts', (): void => {
     expect(result.current.loading).toBe(true)
     await waitForNextUpdate()
     expect(result.current.loading).toBe(false)
-    expect(result.current.error.name).toBe('AbortError')
-    expect(result.current.error.message).toBe('Timeout Error')
+    expect(result.current.error?.name).toBe('AbortError')
+    expect(result.current.error?.message).toBe('Timeout Error')
     expect(onAbort).toBeCalled()
     expect(onTimeout).toBeCalled()
     expect(onAbort).toHaveBeenCalledTimes(1)
@@ -386,8 +386,8 @@ describe('timeouts', (): void => {
     expect(fetch.mock.calls[0][0]).toBe('https://example.com/todos')
     expect(fetch).toHaveBeenCalledTimes(2)
     expect(result.current.loading).toBe(false)
-    expect(result.current.error.name).toBe('AbortError')
-    expect(result.current.error.message).toBe('Timeout Error')
+    expect(result.current.error?.name).toBe('AbortError')
+    expect(result.current.error?.message).toBe('Timeout Error')
     expect(onAbort).toBeCalled()
     expect(onTimeout).toBeCalled()
     expect(onAbort).toHaveBeenCalledTimes(2)

src/types.ts

@@ -133,7 +133,7 @@ export interface Data<TData> {
 export interface ReqBase<TData> {
   data: TData | undefined
   loading: boolean
-  error: Error
+  error: Error | undefined
   cache: Cache
 }
 

src/useMutation.ts

@@ -7,7 +7,7 @@ import { invariant, isString, useURLRequiredInvariant } from './utils'
 type ArrayDestructure<TData = any> = [
   TData | undefined,
   boolean,
-  Error,
+  Error | undefined,
   (variables?: object) => Promise<any>,
 ]
 interface ObjectDestructure<TData = any> extends ReqBase<TData> {

src/useQuery.ts

@@ -7,7 +7,7 @@ import { invariant, isString, useURLRequiredInvariant } from './utils'
 type ArrayDestructure<TData = any> = [
   TData | undefined,
   boolean,
-  Error,
+  Error | undefined,
   (variables?: object) => Promise<any>,
 ]
 interface ObjectDestructure<TData = any> extends ReqBase<TData> {