Data: Experiment with loading logger middleware

packages/data/src/loading-middleware.js

@@ -0,0 +1,55 @@
+/**
+ * Simple loading logging redux middleware.
+ *
+ * @type {import('redux').Middleware}
+ */
+
+const formatLoadedEntry = ( action ) => {
+	let formatted = action.selectorName;
+
+	if ( action.args?.length ) {
+		formatted += ': ' + JSON.stringify( action.args );
+	}
+
+	return formatted;
+};
+
+const getCurrentTime = () => {
+	const date = new Date();
+	return (
+		date.getHours() +
+		':' +
+		date.getMinutes() +
+		':' +
+		date.getSeconds() +
+		'.' +
+		date.getMilliseconds()
+	);
+};
+
+const actionTypeMap = {
+	START_RESOLUTION: 'Started loading',
+	START_RESOLUTIONS: 'Started bulk loading',
+	FINISH_RESOLUTION: 'Finished loading',
+	FINISH_RESOLUTIONS: 'Finished bulk loading',
+	FAIL_RESOLUTION: 'Failed loading',
+	FAIL_RESOLUTIONS: 'Failed bulk loading',
+	INVALIDATE_RESOLUTION: 'Canceled loading',
+};
+
+const loadingMiddleware = () => ( next ) => ( action ) => {
+	if ( actionTypeMap.hasOwnProperty( action.type ) ) {
+		// eslint-disable-next-line no-console
+		console.log(
+			getCurrentTime() +
+				': ' +
+				actionTypeMap[ action.type ] +
+				' ' +
+				formatLoadedEntry( action )
+		);
+	}
+
+	return next( action );
+};
+
+export default loadingMiddleware;

packages/data/src/redux-store/index.js

@@ -16,6 +16,7 @@ import createReduxRoutineMiddleware from '@wordpress/redux-routine';
  */
 import { builtinControls } from '../controls';
 import promise from '../promise-middleware';
+import loadingMiddleware from '../loading-middleware';
 import createResolversCacheMiddleware from '../resolvers-cache-middleware';
 import createThunkMiddleware from './thunk-middleware';
 import metadataReducer from './metadata/reducer';
@@ -242,6 +243,7 @@ function instantiateReduxStore( key, options, registry, thunkArgs ) {
 	const middlewares = [
 		createResolversCacheMiddleware( registry, key ),
 		promise,
+		loadingMiddleware,
 		createReduxRoutineMiddleware( normalizedControls ),
 		createThunkMiddleware( thunkArgs ),
 	];