A simple system for type-safe APIs with examples.

Maybe useful for microservices that do not prefer a heavy framework?

1. Define your type! For input data (payload), please use JSON Schema to define its type; for returned data, just plain TypeScript type is OK.
2. Write your logic! During this, the type definition of your payload and returned data will be inferred by your IDE, and there's no need to worry about typos and TypeErrors.
3. Register your action! Call registerAction to put your fresh code into production.

Although Schema can do much, it cannot do everything. Schema is useful when determining whether the structure of the input data is right, but it knows nothing about your production environment. For example, it does not know whether the object with a given id exists in your database, and this is exactly what your check method should do.

Imagine your check function calls a blocking API to check whether an object with the given id exists, and this API just returns the exact object (if it does exist) instead of telling you whether it exists. (What a bad API! But just think about it.) Your consumer function will use this object, but you certainly do not want to call this blocking API twice. You just want to know whether it exists; but the API just returns the whole object to you. Its action of returning the object is called side effect.

In this case, you can use sideEffect parameter to pass the fetched object directly to the consumer function, without fetching it again.

Guys, we are using TypeScript, not JavaScript. To ensure type safety, we have to wrap the side effect in another parameter. Fortunately, you can customize the structure of the sideEffect parameter passed to your consumer function.