Any way to save TS interface as a plain variable? | TypeScript Community | Page 1

stable jolt Apr 21, 2023, 1:09 PM

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I want to create a form builder, where you can pass it a generic type, and it will create the appropriate inputs, but I'm not sure if it's possible in TS to reference a type as a variable.

type User = {
   name?: string;
   email: string;
   age: string;
}

// item can be null if we're creating a new record, truthy if we're editing
const createForm<T> = ( itemToEdit?: T ) => {
   // somehow save T as a variable (could be a stringified version that i could parse?)
   // so we can determine which fields, and their types to render, which are required, etc.
}

Iterating over itemToEdit doesn't work, bc some keys may be missing from the object, and this needs to be used for creation as well. Thanks!

simple portal Apr 21, 2023, 1:11 PM

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typescript types don't exist at runtime. during compilation they are removed entirely from your code. there's no way to derive a value from a type (but you can go the other way around)

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the way it's usually done is to have a runtime object that represents the User type and derive the type from that. libraries like https://zod.dev/, https://github.com/gcanti/io-ts/, and https://github.com/sinclairzx81/typebox use that approach, if you want some examples

supple berry Apr 21, 2023, 4:43 PM

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There's also https://deepkit.io/ which does provide runtime type information and will let you do the above

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but it comes with runtime overhead

#Any way to save TS interface as a plain variable?