Do not clobber action meta

src/__tests__/promiseMiddleware-test.js

@@ -82,31 +82,83 @@ describe('promiseMiddleware', () => {
       type: resolve('ACTION_TYPE_RESOLVE'),
       payload: foobar,
       meta: {
-        foo2: 'bar2'
+        payload: {
+          foo2: 'bar2'
+        }
       }
     });
   });
 
   it('dispatches reject action with arguments', async () => {
+    try {
+      await dispatch({
+        type: 'ACTION_TYPE_REJECT',
+        payload: {
+          promise: Promise.reject(err),
+          foo3: 'bar3',
+          foo4: 'bar4'
+        }
+      });
+    } catch (e) {
+      // We're not interested in the rejection. We just need to wait until all
+      // dispatching is done.
+      true;
+    }
+
+    expect(baseDispatch.calledTwice).to.be.true;
+
+    expect(baseDispatch.secondCall.args[0]).to.deep.equal({
+      type: reject('ACTION_TYPE_REJECT'),
+      payload: err,
+      meta: {
+        payload: {
+          foo3: 'bar3',
+          foo4: 'bar4'
+        }
+      }
+    });
+  });
+
+  it('does not overwrite any meta arguments', async () => {
     await dispatch({
-      type: 'ACTION_TYPE_REJECT',
+      type: 'ACTION_TYPE_RESOLVE',
       payload: {
-        promise: Promise.reject(err),
-        foo3: 'bar3',
-        foo4: 'bar4'
+        promise: Promise.resolve(foobar),
+        foo2: 'bar2'
+      },
+      meta: {
+        foo3: 'bar3'
       }
     });
 
     expect(baseDispatch.calledTwice).to.be.true;
 
     expect(baseDispatch.secondCall.args[0]).to.deep.equal({
-      type: reject('ACTION_TYPE_REJECT'),
-      payload: err,
+      type: resolve('ACTION_TYPE_RESOLVE'),
+      payload: foobar,
       meta: {
         foo3: 'bar3',
-        foo4: 'bar4'
+        payload: {
+          foo2: 'bar2'
+        }
+      }
+    });
+  });
+
+  it('does not include empty meta payload attribute', async () => {
+    await dispatch({
+      type: 'ACTION_TYPE_RESOLVE',
+      payload: {
+        promise: Promise.resolve(foobar)
       }
     });
+
+    expect(baseDispatch.calledTwice).to.be.true;
+
+    expect(baseDispatch.secondCall.args[0]).to.deep.equal({
+      type: resolve('ACTION_TYPE_RESOLVE'),
+      payload: foobar
+    });
   });
 
   it('returns the original promise from dispatch', () => {
@@ -133,7 +185,7 @@ describe('promiseMiddleware', () => {
         foo2: 'bar2'
       }
     });
-    expect(dispatchedResult).to.eventually.equal(foobar);
+    return expect(dispatchedResult).to.eventually.equal(foobar);
   });
 
   it('reject the original promise from dispatch', () => {
@@ -146,7 +198,7 @@ describe('promiseMiddleware', () => {
         foo2: 'bar2'
       }
     });
-    expect(dispatchedResult).to.eventually.be.rejectedWith(err);
+    return expect(dispatchedResult).to.eventually.be.rejectedWith(err);
   });
 
   it('returns the reject and resolve strings with default values', () => {

src/index.js

@@ -43,23 +43,43 @@ export default function promiseMiddleware(resolvedName, rejectedName) {
 
     dispatch(newAction);
 
+    // Create a base for the next action containing the metadata.
+    let nextActionBase = {
+      meta: {
+        ...action.meta,
+        payload: {
+          ...newAction.payload
+        }
+      }
+    };
+
+    if (Object.keys(nextActionBase.meta.payload).length === 0) {
+      // No arguments were given beside the promise, no need to include them
+      // in the meta.
+      delete nextActionBase.meta.payload;
+    }
+    if (Object.keys(nextActionBase.meta).length === 0) {
+      // No meta was included either, remove all meta.
+      delete nextActionBase.meta;
+    }
+
     // (2) Listen to promise and dispatch payload with new actionName
     return action.payload.promise.then(
       (result) => {
         dispatch({
           type: resolve(action.type, resolvedName),
           payload: result,
-          meta: newAction.payload
+          ...nextActionBase
         });
         return result;
       },
       (error) => {
         dispatch({
           type: reject(action.type, rejectedName),
           payload: error,
-          meta: newAction.payload
+          ...nextActionBase
         });
-        return error;
+        throw error;
       }
     );
   };