#Errors when constructing class based on variables

1 messages · Page 1 of 1 (latest)

potent stratus
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It's a bit hard to describe with words. The problem is that I want to dynamically create/initialize classes. Different classes have different constructor parameters... But somehow I'm not able to get the typing correct.

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thomasjonas#4425
Playground Link

Preview:ts ... const id = "performance-module" const m = modules[id] const copy = {text: "string"} const preperation = m.prepare() // can not get this to work: new m({ copy, ...preperation, }) ...

hasty spoke
#

the problem is the way you're setting up modules using dynamic property names (like [VenueModule.ID]: VenueModule)

#

that treats VenueModule.ID as an arbitrary string rather than the exact literal type, and modules ends up becoming a Record<string, typeof PerformanceModule | typeof VenueModule>

#

if you instead write out the property names, things work out the way you want:

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#
mkantor#7432
Playground Link

Preview:```ts
type Copy = {
text: string
}

type PerformanceModuleConstructor = {
copy: Copy
} & ReturnType<typeof PerformanceModule.prepare>

type VenueModuleConstructor = {
copy: Copy
} & ReturnType<typeof VenueModule.prepare>

class PerformanceModule {
static ID
...```

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potent stratus
#

Wow, amazing. That actually fixes it. Thank you so much!

#

!resolved

tacit shadow
#

Hi @potent stratus and mkantor, I’m Alexander Lill (a real person), a researcher at the University of Zurich. I’m trying to help people receive answers faster on Discord. If you are not ok with giving me some feedback, click the 🚪 symbol, and I will delete this message and apologize for the inconvenience.

#

Would any of the provided links have helped to answer the OPs question? Please click the number-emoji for each link that would have been helpful, and on the ❌ if none of the links would have been helpful to answer the OPs question.

1️⃣ Typescript initialize static variable of a class type
https://stackoverflow.com/questions/24330620

2️⃣ How to use TypeScript constructor to declare variables
https://stackoverflow.com/questions/37550805

3️⃣ Problem when trying to instantiate a class dynamically
https://stackoverflow.com/questions/62735483

Let me know if you have any questions! More info: #1063200184315674706

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#

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potent stratus
#

@hasty spoke hmm, maybe a bit too quick. What if the key that selected the right class is also a variable?

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#
thomasjonas#4425
Playground Link

Preview:ts ... const options = [ "venue-module", "performance-module", ] as Modules[] const id = options[Math.floor(Math.random() * options.length)] const m = modules[id] const copy = {text: "string"} const preperation = m.prepare() // can not get this to work: new m({ copy, ...preperation, }) } ...

hasty spoke
#

i think you'll have to narrow down m to a specific constructor so that typescript can check that the object you pass in is usable. typescript doesn't know how to correlate preparation with the specific m that you use later on

#

here's an example of how you could handle this via narrowing:

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#
mkantor#7432
Playground Link

Preview:```ts
type Copy = {
text: string
}

type PerformanceModuleConstructor = {
copy: Copy
} & ReturnType<typeof PerformanceModule.prepare>

type VenueModuleConstructor = {
copy: Copy
} & ReturnType<typeof VenueModule.prepare>

class PerformanceModule {
static ID
...```

You can choose specific lines to embed by selecting them before copying the link.
hasty spoke
#

i'm not sure if/how you're using modules elsewhere in your code, or what the motivation behind these prepare() methods is, but you might be able to simplify things further

potent stratus
#

I was trying to keep everything as dynamic as possible, but I understand TypeScript does not automagically knows what I mean. I will try to make it a bit simpler. I'm probably overcomplicating things. Thanks again!

tacit shadow
#

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