Typescript type an object with function

Question

I have few functions defined like below and I tried defining the type as : {[key: string]: any } and : {[key: string]: Function } but due to the eslint rules, no-explicit-any and ban-types I couldn't use those type definitions.

The reason for the below structure is that I have a dynamic code that calls the below function based on the value ( ex: someDefinition(someVar), where someVar is based on a value passed)

 const someDefinitions: {[key: string]: any } = {
    A: (v: string): string => 'Returning A',
    B: (v: string): string => 'Returning B with ' + v,
    C: (v: string): string => 'Returning C',
 };

Is there any way to define the types satisfying the rules?

@DanielA.White I assume you mean -> `(value:string) => string` — Keith, Mar 13 '23 at 16:12
A bonus when you get the type correct, `{[key: string]: (a:string) => string }` you'll get implicit types too, so that you can do -> `A: v => 'Returning A',` — Keith, Mar 13 '23 at 16:15
Thanks @Keith, a step forward but I am now getting `'a' is defined but never used.eslint (no-unused-vars)` — Selvakumar Arumugam, Mar 13 '23 at 16:39
@Keith It works just needed to update the rules based on the https://stackoverflow.com/a/56848207/297641. Thanks again. If you could post yours as answer, I could mark it and close. — Selvakumar Arumugam, Mar 13 '23 at 16:55

score 1 · Answer 1 · answered Mar 13 '23 at 16:20

You could create an interface:

interface Foo {
  A(v: string): string;
  B(v: string): string;
  C(v: string): string;
};

Or type:

type Foo = {
  A(v: string): string;
  B(v: string): string;
  C(v: string): string;
};

And use it as the type of someDefinitions:

const someDefinitions: Foo = {
  A: (v: string): string => 'Returning A',
  B: (v: string): string => 'Returning B with ' + v,
  C: (v: string): string => 'Returning C',
};

You can even short-hand the object now that it's typed:

const someDefinitions: Foo = {
  A: (_v) => 'Returning A',
  B: (v) => 'Returning B with ' + v,
  C: (_v) => 'Returning C',
};

Usage:

console.log(someDefinitions.A(''));
console.log(someDefinitions.B('Foo'));
console.log(someDefinitions.C(''));

Thanks. Sorry, I missed to mention the function names in the someDefinition is dynamic and they are based off a keys defined in json. — Selvakumar Arumugam, Mar 13 '23 at 16:36
@SelvakumarArumugam What does the JSON typically look like? Have you tried [`zod`](https://www.totaltypescript.com/tutorials/zod)? — Mr. Polywhirl, Mar 13 '23 at 17:31

Typescript type an object with function

1 Answers1

Usage: