feat: Add identityPayloadCreator helper (#9)

README.md

@@ -29,6 +29,8 @@ export default createActions('example', {
 
   // An action with an argument that also returns a payload.
   setIncrementBy: (n: number) => n,
+  // Which could also be written as this.
+  // setIncrementBy: identityPayloadCreator<number>(),
 
   // An action that returns meta, payload, and even overrides the action type.
   // Note that when you override the action type, the `.actionType` property

src/createReducer.test.ts

@@ -27,5 +27,12 @@ describe('createReducer', () => {
         },
       }),
     )
+
+    state = testReducer(state, testActions.identityPayload('hello world'))
+    expect(state).toEqual(
+      expect.objectContaining({
+        identityPayload: 'hello world',
+      }),
+    )
   })
 })

src/identityPayloadCreator.test.ts

@@ -0,0 +1,11 @@
+import identityPayloadCreator from './identityPayloadCreator'
+
+describe('identityPayloadCreator', () => {
+  it('has one argument which is typed and returned', () => {
+    const payloadCreator = identityPayloadCreator<number>()
+    const payload = payloadCreator(12)
+
+    expect(typeof payload).toBe('number')
+    expect(payload).toBe(12)
+  })
+})

src/identityPayloadCreator.ts

@@ -0,0 +1,5 @@
+function identityPayloadCreator<T>() {
+  return (payload: T) => payload
+}
+
+export default identityPayloadCreator

src/test/testActions.ts

@@ -1,8 +1,10 @@
 import createActions from '../createActions'
+import identityPayloadCreator from '../identityPayloadCreator'
 
 const testActions = createActions('test', {
   noPayload: () => undefined,
   simplePayload: () => 'simple',
+  identityPayload: identityPayloadCreator<string>(),
   complexPayload: (arg1: number, arg2: string) => ({ arg1, arg2 }),
   specialProperties: (arg1: number, arg2: string) => ({
     payload: { arg1, arg2 },

src/test/testReducer.ts

@@ -12,6 +12,7 @@ const initialState = {
     arg1: -1,
     arg2: '',
   },
+  identityPayload: '',
 
   start: '',
   success: '',
@@ -38,6 +39,10 @@ const testReducer = createReducer(initialState, (builder) => {
         arg2: action.payload.arg2,
       },
     }))
+    .addHandler(testActions.identityPayload, (state, action) => ({
+      ...state,
+      identityPayload: action.payload,
+    }))
     .addStartHandler(testActions.promisePayload, (state) => ({
       ...state,
       start: 'started',