Can I get suggestions of all possible properties of an object in TypeScript?

Question

I'm trying to use Telegraf (4.6.0) types and I'm having an issue with exploring possible message properties.

Here's what I do now:

import { Telegraf, Context } from 'telegraf'

const myBot = new Telegraf(myToken)
listenerBot.on('message', (ctx: Context) => {
    const {
        text,
        forward_from_chat, forward_from_message_id,
        photo, caption, caption_entities,
        // what it will contain if there's a video? audio? document? ...
    } = ctx.message as any
    // do stuff with message
}

Since messages can be of various types (in both non-TS and TS sense), when I type ctx.message. in IDE (VS Code in my case) I'm only suggested the props that are always in message object (like message_id). Yes, I can do things like

if('text' in ctx.message) {
    // do stuff with ctx.message.text
}

but this doesn't help me explore what props can ctx.message hold. I can imagine a hacky way like

class ExploredContext = ExploreProps<Context> → gives a class similar to Context,
  but all possible props are non-optional

...
(ctx as ExploredContext).message._ // cursor here, IDE shows possilbe props
(ctx.message as ExploredMessage)._ // or like this

but neither I know how to implement things like ExploreProps helper (I'm only aware of utility types) nor I know any better, non-hacky ways to get this (like some configuration of typescript and/or IDE).

Can you suggest a way to implement ExploreProps or a better way to explore possible props?

(in Telegraf context, I've also asked at in an issue, but a consistent solution would be helpful without regard to Telegraf itself)

Answer 1

You can flatten a union using StrictUnion as defined here This type will basically add the missing members to all union constituents with the type undefined. This will allow de-structuring to suggest all members from any constituent, but each member that is not present in all union constituents will also contain undefined (which is probably for the best from a type-safety perspective)

import { Telegraf, Context } from 'telegraf'

type UnionKeys<T> = T extends T ? keyof T : never;
type StrictUnionHelper<T, TAll> = T extends any ? T & Partial<Record<Exclude<UnionKeys<TAll>, keyof T>, undefined>> : never;
type StrictUnion<T> = StrictUnionHelper<T, T>


const myToken = ""
const myBot = new Telegraf(myToken)
myBot.on('message', (ctx: Context) => {
    const {
        text,
        forward_from_chat, forward_from_message_id,
        photo, caption, caption_entities,
        
    } = ctx.message as StrictUnion<Context['message']>
})

Playground Link