Error Handling and Running an App
Good web applications must have informative error messages to notify clients exactly why their request has failed. Errors might be caused either by the client (e.g., wrong input data) or by the server (e.g., a bug in the code).
The client might be a browser, in which case the application should display an HTML page. For example, a 404 page should display when the requested resource is not found. Or the client might be another application consuming our resources via the REST API. In this case, the application should send the appropriate HTTP status code and the message in the JSON format (or XML or another ...