Type Redux store and middleware (#24843)

app/javascript/mastodon/store/middlewares/errors.ts

@@ -0,0 +1,18 @@
+import { Middleware } from 'redux';
+import { showAlertForError } from '../../actions/alerts';
+import { RootState } from '..';
+
+const defaultFailSuffix = 'FAIL';
+
+export const errorsMiddleware: Middleware<Record<string, never>, RootState> =
+  ({ dispatch }) => next => action => {
+    if (action.type && !action.skipAlert) {
+      const isFail = new RegExp(`${defaultFailSuffix}$`, 'g');
+
+      if (action.type.match(isFail)) {
+        dispatch(showAlertForError(action.error, action.skipNotFound));
+      }
+    }
+
+    return next(action);
+  };