feat(meta): add metadata support

README.md

@@ -97,6 +97,23 @@ Note that if you try and use the base function in a reducer, an error will be th
 case String(fetchData): // throws an error
 ```
 
+#### Metadata
+
+You can add metadata to any action given a function that will receive the same arguments as the payload creator:
+
+```js
+import { createAsyncAction } from 'redux-promise-middleware-actions';
+
+export const fetchData = createAsyncAction(
+  'FETCH_DATA',
+  (n: number) => fetch(...),
+  (n: number) => ({ n })
+);
+
+
+dispatch(fetchData(42)); // { type: 'FETCH_DATA_PENDING', meta: { n: 42 } }
+```
+
 ### Async reducer
 
 You can now handle the different events in your reducer by referencing the possible outcome states:

src/actions.ts

@@ -2,10 +2,11 @@ export const onPending = (type: any) => `${type}_PENDING`;
 export const onFulfilled = (type: any) => `${type}_FULFILLED`;
 export const onRejected = (type: any) => `${type}_REJECTED`;
 
-export interface IAction<Payload> {
+export interface IAction<Payload, Metadata = undefined> {
   type: string;
   payload?: Payload;
   error?: boolean;
+  meta?: Metadata;
 }
 
 export function createAction(
@@ -17,14 +18,22 @@ export function createAction<Payload, U extends any[]>(
   payloadCreator: (...args: U) => Payload
 ): (...args: U) => IAction<Payload>;
 
-export function createAction<Payload, U extends any[]>(
+export function createAction<Payload, Metadata, U extends any[]>(
+  type: string,
+  payloadCreator: (...args: U) => Payload,
+  metadataCreator?: (...args: U) => Metadata
+): (...args: U) => IAction<Payload, Metadata>;
+
+export function createAction<Payload, Metadata, U extends any[]>(
   type: string,
-  payloadCreator?: (...args: U) => Payload
-): (...args: U) => IAction<Payload> {
+  payloadCreator?: (...args: U) => Payload,
+  metadataCreator?: (...args: U) => Metadata
+): (...args: U) => IAction<Payload, Metadata> {
   return Object.assign(
     (...args: U) => ({
       type,
       ...(payloadCreator && { payload: payloadCreator(...args) }),
+      ...(metadataCreator && { meta: metadataCreator(...args) }),
     }),
     { toString: () => type }
   );
@@ -36,12 +45,13 @@ export interface IAsyncActionFunction<Payload> extends Function {
   rejected: (payload?: any) => IAction<any>;
 }
 
-export function createAsyncAction<Payload, U extends any[]>(
+export function createAsyncAction<Payload, Metadata, U extends any[]>(
   type: string,
-  payloadCreator: (...args: U) => Promise<Payload>
+  payloadCreator: (...args: U) => Promise<Payload>,
+  metadataCreator?: (...args: U) => Metadata
 ) {
   return Object.assign(
-    createAction(type, payloadCreator),
+    createAction(type, payloadCreator, metadataCreator),
     {
       toString: () => {
         throw new Error(`Async action ${type} must be handled with pending, fulfilled or rejected`);

test/actions.test.ts

@@ -30,6 +30,40 @@ describe('actions', () => {
       const action = createAction(TYPE, (a: number, b: number) => a + b);
       assert.equal(action(40, 2).payload, 42);
     });
+
+    describe('metadataCreator', () => {
+      it('should not have metadata', () => {
+        const action = createAction(TYPE, (n: number) => ({ n }));
+        assert.equal('meta' in action(42), false);
+      });
+
+      it('should forward same payload and metadata', () => {
+        const action = createAction(TYPE, (n: number) => ({ n }), (n: number) => ({ n }));
+        assert.deepEqual(action(42), {
+          type: TYPE,
+          payload: { n: 42 },
+          meta: { n: 42 },
+        });
+      });
+
+      it('should have different payload and metadata', () => {
+        const action = createAction(TYPE, (n: number) => ({ n }), () => ({ asdf: 1234 }));
+        assert.deepEqual(action(42), {
+          type: TYPE,
+          payload: { n: 42 },
+          meta: { asdf: 1234 },
+        });
+      });
+
+      it('should have only metadata', () => {
+        const action = createAction(TYPE, () => undefined, () => ({ asdf: 1234 }));
+        assert.deepEqual(action(), {
+          type: TYPE,
+          payload: undefined,
+          meta: { asdf: 1234 },
+        });
+      });
+    });
   });
 
   describe('createAsyncAction', () => {