TypeScript: Contributing Fastest-Validator Schema Inference and a 'Global Action Index'

[Laurin-W]

Hi, I found a way to create a decentralized global 'index' of all service actions so that TypeScript provides you with a list of all actions, their parameters, and their return types (thanks to @Telokis for the inspiration).

Implementation Idea

The idea is to make the moleculer namespace global and in each service definition file to add the service to the global namespace (using interface merging). With that, the required changes are quite small and I can provide a codemod for applying them.

In the following example of a service definition file, you can see how typeof testService1 is merged into the AllServices interface. testService1 needs to be typed using satisfies ServiceSchema.

const testService1 = {
  version: 1,
  name: 'test-service',
  actions: {
    action1: {
      params: { p1: {type: 'string'} },
      handler(ctx) { return "..."; }
  }
} satisfies ServiceSchema;

declare global {
  export namespace Moleculer {
    export interface AllServices {
      serviceKeyXYZ: typeof testService1;
    }
  }
}

That's the only modification necessary.

With type-mapping, you can convert the fastest-validator params schema objects into typescript types.

Also using type-mapping, you can create a type from AllServices that contains all actions in the format { [<serviceVersion>.<serviceName>.<actionName>]: ActionSchema | ActionHandler } .
From there, you can construct a ctx.call signature that provides all actions and knows their parameter and return types. Adding parameter doc strings is possible, too.

To enable parameter type inference of ctx.params in an action handler ifself, you need to wrap the action in a defineAction function that does nothing but to inform typescript that ctx.params should be inferred from the params schema. (If you have advanced TypeScript experience, I'm running into issues here, and I'd appreciate your help.)

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For our project, ActivityPods, we are going to use this feature since it is a big pain to find service actions, their return types, and their required parameters.

I would like to share this work with the community and wonder how to do so. Should I create a separate npm library (perhaps the most straight forward option?) or make a PR to this repository?

Best,
Laurin

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Cross-linking:

• Improve type definitions to allow strict type-checking of ctx.call, actions definitions and events #822
• Feature Request - Complete TypeScript Implementation #1216
• Enhance the moleculer ecosystem #1204 (type decorators for services)

[icebob]

Good idea, I was thinking about a similar solution for version 1.0 of Moleculer where there is a global interface to store the action definitions with augmenting. But in my mind, I thought just you should extend it in each services, and just get the param types for ctx.call generics. Your version looks better if we can do the same things automatically.

Please create a PR with your idea but for the next (0.15) branch instead of master.

[Laurin-W]

Great! I'll create a PR when I'm ready :)

[icebob]

Any news about it?

[Laurin-W]

Hi @icebob, sorry for the late reply. I asked NLNet if I could get an extension on our grant that we have for ActivityPods. Unfortunately, I haven't heard back from them so far and I can't start before they give the go for it. I sent another mail the other day and will inform you once I know more.

Do you have time pressure on this?

[icebob]

Nop, but in this case I think it can be implemented after 0.15 only

[Laurin-W]

FYI:

I got green light from NLNet :)

As a first step, I created a draft PR in the fastest-validator repo icebob/fastest-validator#355 for inferring TS types from schemas.