hndl
v2.1.2
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A simple node framework, you've been looking for
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HNDL
Are you looking for a new Node framework? Well, you've come to the right place!
HNDL was made to address my personal frustrations with existing Node frameworks, and here are the main design decisions behind HNDL:
- No middleware
- Strong types
- Simple routing
- Async by default
- No external dependencies
- Sane defaults
No Middleware?!
Yes! This is my main point of concern with existing Node frameworks. Let's take a typicial Express request handler:
app.get("/timestamp", (req, res) => {
res.send({
timestamp: new Date().valueOf();
})
});
Let's say we send a request GET /timestamp
, what would the response be?
It would be valid to say: "Well it returns a json object containing a unix millis timestamp.". However it's not correct, because you don't know that before I registered this handler, I also have:
app.use((req, res) => {
res.sendStatus(400);
})
So to avoid confusion like this, there is no middleware support in HNDL. If your request handler gets invoked, it is guaranteed to be THE ONLY thing that will process this event. Isn't that cool? Why do I even have to sell this as a feature? How did we come to this?
Endpoint Type Definition
In HNDL any object that looks like this is a valid endpoint:
type Endpoint<T> = {
accept: (request: Request) => Optional<T> | Promise<Optional<T>>;
handle: (payload: T) => Response | Promise<Response>;
}
The most important thing to notice is the relationship between accept
and handle
:
handle
takes as a param whatever accept
returns.
How they are related is explained in the next section about routing.
Routing
A router in HNDL is defined using the function router
, it takes a variadic list of
endpoints like this:
const myRouter = router(
firstEndpoint,
secondEndpoint,
thirdEndpoint
)
The main job of the router is to choose one of the passed endpoints to handle the
incoming request. And for this the router uses the accept
function.
So when a new request comes in, the router will go in order, and call the accept
function of every endpoint. The first accept
that returns a truthy value, is chosen.
Whatever this truthy value is, the router will invoke the handle
method of this chosen
endpoint with that value.
The handle
method of the chosen endpoint MUST return a Response
object.
In other words, if you accept the request, you must handle it entirely.
Both accept
and handle
can of course be async.
Finally, it's worth noting that the router
function just returns another
Endpoint
so they can be nested, if needed, but this is discouraged.
Examples
Let's go through a few examples to illustrate how this works:
This endpoint will respond to any request with a 200 OK:
const everythingIsOK = {
accept: () => true,
handle: () => { status: OK }
}
This router will respond with 200 OK
if the URL starts with /ok
,
otherwise with 404 Not Found
:
const myRouter = router(
{
accept: request => request.url.startsWith("/ok"),
handle: () => { status: OK }
},
{
accept: () => true,
handle: () { status: NOT_FOUND }
}
)
The Service
When developing a web service it's necessary to perform additional
tasks such as logging, error handling, etc... These do not fall
into the area of responsibility of endpoints, and for this we use the service
.
The service
function takes the following arguments:
type ServiceProps = {
endpoint: Endpoint<any>;
errorHandler?: ErrorHandler;
logger?: Logger;
}
type ErrorHandler = (error: any) => Response | Promise<Response>;
type Logger = (request: Request, response: Response) => void;
And returns a new endpoint
which will log requests and handle
errors correctly thrown from both the accept
and handle
functions
of the passed endpoint.
It's a convenient function that is not strictly necessary in this package, but is something that most people will like to have.
The Listener
The last piece of the puzzle is the listener
. It is meant to conform
to the request handler function passed into the createServer
function
which comes with the default node http
module.
The listener's job is to simply allow async handling of incoming requests. And can be used in the following way:
const myEndpoint: Endpoint = { /* ... */};
const server = createServer(listener(myEndpoint));