[TS] Defining the handler and the return type

[jaclas]

Runtime

Node

Runtime version

18

Module version

21.3.3

Used with

standalone

Any other relevant information

No response

How can we help?

I would like the handler to explicitly return the DataResultObject type (my object type), the handler type declaration in Hapi looks like this:

export namespace Lifecycle {
    /**
     * Lifecycle methods are the interface between the framework and the application. Many of the request lifecycle steps:
     * extensions, authentication, handlers, pre-handler methods, and failAction function values are lifecycle methods
     * provided by the developer and executed by the framework.
     * Each lifecycle method is a function with the signature await function(request, h, [err]) where:
     * * request - the request object.
     * * h - the response toolkit the handler must call to set a response and return control back to the framework.
     * * err - an error object available only when the method is used as a failAction value.
     */
    type Method<
        Refs extends ReqRef = ReqRefDefaults,
        R extends ReturnValue<any> = ReturnValue<Refs>
    > = (
            this: MergeRefs<Refs>['Bind'],
            request: Request<Refs>,
            h: ResponseToolkit<Refs>,
            err?: Error | undefined
        ) => R;

So I declare the route object like this:

const poemsRoutings: ServerRoute<ReqRefDefaults, DataResultsObject>[] = [
    {
        method: "GET",
        path: "/api/poems/pages/count",
        options: {
            handler: poems.getPoemsPagesCountHandler,
            auth: {
                mode: "try"
            }
        }
    },

and the environment (vscode) correctly develops this type, showing that my type will be returned:

But at the same time, I get a TS compilation error (which you can also see in the screenshot) that reads:

Generic type 'ServerRoute<Refs>' requires between 0 and 1 type arguments.ts(2707)

How to do this correctly?

[otajor]

@jaclas the ServerRoute type is different from the handler type. ServerRoute is the type for the entire config object, including method, path etc - it takes 0 or 1 type arguments. handler is the type for the handler function only, which can take 2 type arguments.

To type the handler properly I think you just need to put the correct return type on your poems.getPoemsPagesCountHandler function. It looks like Typescript is already correctly picking up the return type, which is unrelated to you passing it to ServerRoute, so maybe you're doing this already.

[damusix]

If you want to separate your handlers out to some sort of controller abstract, you need to type them accordingly. For this, you can use the Lifecycle namespace. Both Lifecycle.Method and ServerRoute receive the References generic, which you can use to augment the route. See the playground link below:

@jaclas @RodolpheGohard @otajor

https://www.typescriptlang.org/play/?#code/JYWwDg9gTgLgBACQIZmAGjgbzgZQKZQBuBAShAK4x4YAywAZngMYCeTANnnAL5z1QQQcAOQABABYpgAekmphAbgCwAKFUwWYLgAUIeECTz0AznAC8WVXDgBFcgRYAuSyuvWmSKgHNoLAPzOxjBQwAB2XlY8qtyqqkwQoUFwXngwuvrG2kgpxgDCFKEwyKEAJpxQznSMrBx4AHQAsqniECUAPOkGRsYAfOZwABRQeACOGOIAlOZ9mLGucPGJ8KH9AKzKavPDI3Uj9lAsdR7evuZmFsJIoSww4mFewnPWwzDkUCuh0RtxCUnx5IVOsZnPgiKQKFQOnouiY+hZZvMQM1Ws5hCkYMI0JEwJ5xKjpFJpJAMkTsnhjNJ-oVMZFJKVys50UCsjl8gCilcygQsfMIGAYMBfs4EW44EhKHiXKLrCBWnhUcEWI95tYYvM1Wqfks4MSDBDyf0ANqRKlpaHGVQAXQUQA