Convert Redux custom middleware to TypeScript

app/soapbox/middleware/errors.ts

@@ -0,0 +1,29 @@
+import { showAlertForError } from '../actions/alerts';
+
+import type { AnyAction } from 'redux';
+import type { ThunkMiddleware } from 'redux-thunk';
+
+/** Whether the action is considered a failure. */
+const isFailType = (type: string): boolean => type.endsWith('_FAIL');
+
+/** Whether the action is a failure to fetch from browser storage. */
+const isRememberFailType = (type: string): boolean => type.endsWith('_REMEMBER_FAIL');
+
+/** Whether the error contains an Axios response. */
+const hasResponse = (error: any): boolean => Boolean(error && error.response);
+
+/** Whether the error should be shown to the user. */
+const shouldShowError = ({ type, skipAlert, error }: AnyAction): boolean => {
+  return !skipAlert && hasResponse(error) && isFailType(type) && !isRememberFailType(type);
+};
+
+/** Middleware to display Redux errors to the user. */
+export default function errorsMiddleware(): ThunkMiddleware {
+  return ({ dispatch }) => next => action => {
+    if (shouldShowError(action)) {
+      dispatch(showAlertForError(action.error));
+    }
+
+    return next(action);
+  };
+}