JavaScript

I have a function, that takes among other things an object of functions:

type ForMembers<S> = {
 [Key: string]: (arg: S) => void;
};

export default function transform<S extends { [index: string]: any }, D extends { [index: string]: any }>(
  source: S,
  interfaceName: string,
  forMembers?: ForMembers<S>
): D {
  const newObj = extract(source, getKeys(interfaceName));
  if (forMembers) {
    Object.keys(forMembers).forEach((key) => forMembers[key](newObj));
  }
  return newObj as unknown as D;
}

The idea is that i can pass any object of functions that i want, but typescript for some reason requires that i pass all the properties that exist on type , otherwise it throws an error

For instance if D is

interface Destination {
name: string;
bio: string;
names: string[];
profession: {
  field: string;
  level: string;
  };

And i call the function as:

transform<Source, Destination>(sourceData, "Destination", {
  name: () => {},
  bio: () => {},
  profession: () => {},
});
}

It will throw an error:

Argument of type ‘{ name: () => void; bio: () => void; profession: () => void; }’ is not assignable to parameter of type ‘ForMembers<Destination, Source>’. Property ‘names’ is missing in type ‘{ name: () => void; bio: () => void; profession: () => void; }’ but required in type ‘ForMembers<Destination, Source>’.

If i add the missing property – ‘names’, the error goes away, however i want to pass only the properties i need, not all of them. So the question is this – How to make the function to take as forMembers any combination of properties of D, not necessarily all of them?

Answer

You can tell TS that all properties of an object are optional, using Partial:

forMembers?: Partial<ForMembers<S>>

How to resolve – Argument of type is not assignable to type – TYPESCRIPT

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Answer