How to extend the Response in Opine (Deno framework)?

Question

first question here.

Does anyone know how to extend the response in Opine (Deno framework) so that I can create custom responses?

For example I would like to create:

res.success(message)

So that I don't need to set HTTP codes every time like this:

res.setStatus(200).json({data: "success" });

I tried extending the response like it's done here: https://deno.land/x/opine@2.1.5/test/units/app.response.test.ts

This is my code:

import { opine } from "https://deno.land/x/opine@2.1.4/mod.ts";

const app = opine();

(app.response as any).shout = function (str: string) {
    this.send(str.toUpperCase());
};

app.get("/", (req, res) => {
    res.shout("hello")
})

app.listen(3000);
console.log("Opine started on port 3000");

export { app };

But when I run the program I get:

error: TS2339 [ERROR]: Property 'shout' does not exist on type 'OpineResponse<any>'.
    res.shout("hello")
        ~~~~~

Thank you.

`as any` should always work. Please [edit] your question to include the code that you tried. — Bergi, Apr 24 '22 at 21:12
You might be looking for interface declaration merging though — Bergi, Apr 24 '22 at 21:12
@Bergi Thank you for your reply. I edited my question with my code and the error detail. — floco, Apr 24 '22 at 21:32
The unit test code you linked uses `(res as any).shout("hey");` — Bergi, Apr 24 '22 at 23:09

score 0 · Accepted Answer · answered Apr 25 '22 at 04:02

There's not really a "clean" way of doing this without forking opine and modifying the functions and methods which are core to the library.

You can satisfy the compiler by asserting the types at the invocation sites (e.g. by using any just like in the test file to which you linked). Another approach is to use an assertion function like in the example refactor of your code below:

so-71990454.ts:

import { assert } from "https://deno.land/std@0.136.0/testing/asserts.ts";
import {
  type Opine,
  opine,
  type OpineResponse,
} from "https://deno.land/x/opine@2.1.5/mod.ts";

// Define the type extensions here
type ExtendedOpineResponse = {
  shout(body: string): void;
};

// Implement the extensions here
function extendOpineApp(app: Opine): void {
  // deno-lint-ignore no-explicit-any
  (app.response as any).shout = function (str: string) {
    this.send(str.toUpperCase());
  };
}

// Assert feature tests for each one in this function
function assertIsExtendedResponse<T extends OpineResponse>(
  response: T,
): asserts response is T & ExtendedOpineResponse {
  assert(
    // deno-lint-ignore no-explicit-any
    typeof (response as any).shout === "function",
    'Method "shout" not found on response',
  );
}

export const app = opine();
// Invoke the extending function after creating the app
extendOpineApp(app);

app.get("/", (_req, res) => {
  assertIsExtendedResponse(res);
  res.shout("hello");
});

app.listen(3000);
console.log("Opine started on port 3000");

You can see that type-checking the module produces no diagnostic errors:

$ deno --version
deno 1.21.0 (release, x86_64-unknown-linux-gnu)
v8 10.0.139.17
typescript 4.6.2

$ deno check so-71990454.ts

$ echo $?
0

How to extend the Response in Opine (Deno framework)?

1 Answers1