Grabbed dndbeyond's source code

```
~/go/bin/sourcemapper -output ddb -jsurl https://media.dndbeyond.com/character-app/static/js/main.90aa78c5.js
```

ddb_main/tools/js/Shared/reducers/toastMessage.ts

@@ -0,0 +1,109 @@
+import * as actionTypes from "../actions/toastMessage/actionTypes";
+import { ToastMessageAction } from "../actions/toastMessage/typings";
+import {
+  MessageState,
+  ToastMessageMetaState,
+  ToastMessageState,
+  ToastState,
+} from "../stores/typings";
+
+const initialMessagePayloadState: ToastState = {
+  title: "",
+  message: "",
+};
+
+/**
+ *
+ * @param state
+ * @param action
+ */
+function messagePayload(
+  state: ToastState = initialMessagePayloadState,
+  action: ToastMessageAction
+): ToastState {
+  switch (action.type) {
+    case actionTypes.ADD_MESSAGE:
+      return {
+        ...state,
+        ...action.payload.toast,
+      };
+  }
+  return state;
+}
+
+const initialMessageMetaState: ToastMessageMetaState = {
+  level: "info",
+  autoDismiss: 5,
+  dismissible: true,
+  position: "bc",
+};
+
+/**
+ *
+ * @param state
+ * @param action
+ */
+function messageMeta(
+  state: ToastMessageMetaState = initialMessageMetaState,
+  action: ToastMessageAction
+): ToastMessageMetaState {
+  switch (action.type) {
+    case actionTypes.ADD_MESSAGE:
+      return {
+        ...state,
+        ...action.payload.meta,
+      };
+  }
+  return state;
+}
+
+const initialMessageState: MessageState = {
+  payload: initialMessagePayloadState,
+  meta: {},
+};
+function message(
+  state: MessageState = initialMessageState,
+  action: ToastMessageAction
+): MessageState {
+  switch (action.type) {
+    case actionTypes.ADD_MESSAGE:
+      return {
+        ...state,
+        payload: messagePayload(undefined, action),
+        meta: messageMeta(undefined, action),
+      };
+  }
+  return state;
+}
+
+let messageId: number = 0;
+
+/**
+ *
+ * @param state
+ * @param action
+ */
+function toastMessage(
+  state: ToastMessageState = {},
+  action: ToastMessageAction
+): ToastMessageState {
+  switch (action.type) {
+    case actionTypes.ADD_MESSAGE:
+      messageId++;
+      return {
+        [messageId]: message(undefined, action),
+      };
+
+    case actionTypes.REMOVE_MESSAGE:
+      let newState: ToastMessageState = {};
+      Object.keys(state).forEach((messageId) => {
+        if (messageId !== action.payload.id) {
+          newState[messageId] = state[messageId];
+        }
+      });
+      return newState;
+  }
+  return state;
+}
+
+export default toastMessage;