[BUG] TS2339: Property 'on' does not exist on type.

[sebastien-savalle]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

We observed a weird behavior when migrating to cds 8 and cds-types 0.7.0.

Custom handler cannot be registered properly. A typescript error is thrown.

error TS2339: Property 'on' does not exist on type 'AdminService'.

import { ApplicationService } from '@sap/cds';

export default class AdminService extends ApplicationService {
  init() {
    this.on('health', () => {
      return { status: 'UP' };
    });
  }
}

But it works when this is cast to ApplicationService.

import { ApplicationService } from '@sap/cds';

export default class AdminService extends ApplicationService {
  init() {
    (this as ApplicationService).on('health', () => {
      return { status: 'UP' };
    });
  }
}

Expected Behavior

No response

References

https://pages.github.tools.sap/cap/docs/tools/cds-typer#typer-top-level-imports

Versions

backend	https://github.com/<your/repo>
@cap-js/asyncapi	1.0.2
@cap-js/audit-logging	0.8.1
@cap-js/cds-types	0.7.0
@cap-js/db-service	1.14.1
@cap-js/hana	1.4.1
@cap-js/openapi	1.0.7
@cap-js/sqlite	1.7.6
@cap-js/telemetry	1.0.1
@sap/cds	8.4.0
@sap/cds-compiler	5.4.0
@sap/cds-dk	8.4.0
@sap/cds-dk (global)	8.4.0
@sap/cds-fiori	1.2.7
@sap/cds-foss	5.0.1
@sap/cds-mtxs	2.3.0
@sap/eslint-plugin-cds	3.0.4
Node.js	v20.15.1

Anything else? Logs?

No response

[sebastien-savalle]

Same code works with cds-types 0.6.5 :(

[daogrady]

Hi Sébastien,

thanks for reporting this issue!
This looks a bit like TS is trying to infer the type from the implementation files, which would imply you don't have cds-types installed in your project.
Please note that since cds8, @cap-js/cds-types has to be installed explicitly and is no longer pulled in from @sap/cds.
Did you add @cap-js/cds-types as devDependency to your project and install it?

Best,
Daniel

[daogrady]

Actually, I am pretty sure this is a duplicate of #251

If you do have cds-types installed, can you please run (p)npm rebuild in your project and see, if that fixes the problem?

[sebastien-savalle]

Hi Daniel,

Yes, we do have cds-types installed as you can see in the summary.
We use pnpm, so this might be similar to the issue you mentioned.

But, this works well with version 0.6.5.

[daogrady]

Hi Sébastien,

thanks for checking! Please also check out my other suggestion.

Best,
Daniel

[hakimio]

pnpm rebuild doesn't fix the issue. Most likely because of the issue with pnpm: #251 (comment)

[daogrady]

Hi Sébastien,

can you please check out @hakimio's suggestion and see if that solves the problem for you?
If it does, could you please also elaborate a bit on your setup? Do you use a monorepo? If so, do the submodules of that monorepo have a dependency on cds-types?

Best,
Daniel

[sebastien-savalle]

Hi Daniel,

First of all regarding our project setup:

• We have a monorepo managed by pnpm
• We added cds-types as a dev dependency in every submodules and also in root package

I tried a few things to make it work:

1. As suggested, I put @cap-js/cds-types as types:

2. Then, I tried with "./node_modules/@cap-js/cds-types"

3 Finally, I found another workaround by adding cds-types as typeRoots like

[hakimio]

@sebastien-savalle how does your tsconfig look like? Does the types config work if you set moduleResolution to NodeNext?

[sebastien-savalle]

No, this does not work even with moduleResolution set to NodeNext

And pnpm rebuild is sometimes helpful when everything looks broken.

tsconfig:

{
  "compilerOptions": {
    "target": "es2019",
    "module": "nodenext",
    "outDir": "./gen",
    "rootDir": "./",
    "baseUrl": ".",
    "moduleResolution": "nodenext",
    "skipLibCheck": true,
    "preserveConstEnums": true,
    "sourceMap": true,
    "allowJs": true,
    "strict": true,
    "strictNullChecks": true,
    "strictPropertyInitialization": false,
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true,
    "noImplicitAny": false,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "types": [
      "node",
      "jest",
      "express"
    ],
    "typeRoots": [
      "./types",
      "./node_modules/@types",
      "./node_modules/@cap-js/cds-types"
    ]
  },
  "include": [
    "../.eslintrc.json",
    "./srv/**/*.ts",
    "./types/**/**.d.ts",
    "./test/**/*.ts"
  ]
}