always return PayloadAction from PayloadActionCreator

reduxjs · Jul 16, 2019 · a960dc6 · a960dc6
1 parent aec760c
commit a960dc6
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Showing 2 changed files with 12 additions and 27 deletions.
diff --git a/src/createAction.ts b/src/createAction.ts
@@ -24,26 +24,11 @@ export type PayloadActionCreator<P = any, T extends string = string> = { type: T
   * of contra-variant types.
   */
   [undefined] extends [P] ? {
-    // not sure which behavious fits better
-
-    /*
-    * actionCreator() => Action<T>
-    * actionCreator(undefined) => Action<T>
-    * actionCreator("foo") => PayloadAction<"foo", T>
-    */
-    (payload?: undefined): Action<T>
+    (payload?: undefined): PayloadAction<undefined, T>
     <PT extends Diff<P, undefined>>(payload?: PT): PayloadAction<PT, T>
-
-    /*
-    * actionCreator() => Action<T>
-    * actionCreator(undefined) => PayloadAction<undefined, T>
-    * actionCreator("foo") => PayloadAction<"foo", T>
-    */
-    // (): Action<T>
-    // <PT extends P>(payload: PT): PayloadAction<PT, T>
   }
   : [void] extends [P] ? {
-    (): Action<T>
+    (): PayloadAction<undefined, T>
   }
   : {
     <PT extends P>(payload: PT): PayloadAction<PT, T>
@@ -62,7 +47,7 @@ export type PayloadActionCreator<P = any, T extends string = string> = { type: T
 export function createAction<P = any, T extends string = string>(
   type: T
 ): PayloadActionCreator<P, T> {
-  function actionCreator(payload?: P): Action<T> | PayloadAction<P, T> {
+  function actionCreator(payload?: P): PayloadAction<undefined | P, T> {
     return { type, payload }
   }
 

diff --git a/type-tests/files/createAction.typetest.ts b/type-tests/files/createAction.typetest.ts
@@ -7,6 +7,8 @@ import {
   AnyAction
 } from 'redux-starter-kit'
 
+function expectType<T>(p: T) { }
+
 /* PayloadAction */
 
 /*
@@ -50,7 +52,7 @@ import {
 /* PayloadActionCreator */
 
 /*
- * Test: PayloadActionCreator returns Action or PayloadAction depending
+ * Test: PayloadActionCreator returns correctly typed PayloadAction depending
  * on whether a payload is passed.
  */
 {
@@ -62,16 +64,14 @@ import {
     { type: 'action' }
   ) as PayloadActionCreator
 
-  let action: Action
-  let payloadAction: PayloadAction
-
-  action = actionCreator()
-  action = actionCreator(undefined)
-  action = actionCreator(1)
-  payloadAction = actionCreator(1)
+  expectType<PayloadAction<number>>(actionCreator(1));
+  expectType<PayloadAction<undefined>>(actionCreator());
+  expectType<PayloadAction<undefined>>(actionCreator(undefined));
 
   // typings:expect-error
-  payloadAction = actionCreator()
+  expectType<PayloadAction<number>>(actionCreator());
+  // typings:expect-error
+  expectType<PayloadAction<undefined>>(actionCreator(1));
 }
 
 /*