FP Interceptor
Formulaic’s data types library (FP) can be used just on the backend for internal structure, but it excels when used to format outgoing responses in conjunction with the FP Interceptor.
The FPInterceptor simply intercepts outgoing responses, and uses FP, class-validator, and class-transformer methods under the hood to filter, transform, and format outgoing responses.
Background
Formulaic’s FP library defines an standardized object structure that makes it easy and safe to work with data, both at compile time through type statements, and also contains data inside objects that allows for run-time type checking and discrimination of data types.
Learn more about FP in the FP module documentation.
Features
Easy Flow Control
FP provides great control over data flow, with strongly typed data, even in places where JavaScript/TypeScript throws away type data (Promise rejection, try/catch error statements),
and comes with utilities like unless, mapIf, and more that allow easy implementation of default values and error recovery backup flows.
Strongly Typed Client Generation
Many OpenAPI client generators do not type error responses, likely because rejected Promises and
catch statements have no easy way to be strongly typed.
FP allows for all data to be transmitted as success data (documented as a union type in OpenAPI), and makes it easy to distinguish success cases from various error causes on the front-end.
Better Debug Data Visibility
There are many places where the backend holds data that would be useful for developers, yet presents privacy or security risks to share with the user.
FP Interceptor makes use of class-transformer under the hood, configured to strip out any data
not explicitly marked as information to send to the client.
This enables a number of benefits when using FPInterceptor:
Improved Log Output
Error responses, like DatabaseException, can include the entire exception message
and stacktrace to be included in logs, without the user seeing the cause.
Dev-Only Output
FPInterceptor uses class-transformer configuration (namely, groups), to transform
and conditionally include information in responses.
By default, FPInterceptor uses the NODE_ENV environment variable, and will automatically
include more verbose information if the server is explicitly running in "development" mode.