Get the return type from a method parameter

I would like to get the of the return type from a method where I pass the key as a parameter and the return is type from the interface.

I looked at this answer Is there a way to "extract" the type of TypeScript interface property? and the way the answers seem to show is when you use a string literal. I however don’t know what the string will be passed in as. How can get the type without knowing what the parameter will be?

Here is the closes I have gotten based on the above answer, but it still shows an error

Type ‘T’ cannot be used to index type ‘Partial<GameOptions>’.

interface GameOptions {
  production: boolean;
  background: string;
  stats?: boolean;
  objects?: new() => object
}

export class MyClass {
  // Set through a method in another class constructor
  #options: Partial<GameOptions> = {};

  get<T = keyof GameOptions>(option: T): GameOptions[keyof GameOptions] {
    return this.#options[option];
  }
}

this.#production = this.gameConfig.get('production');

Type ‘string | boolean | new() => object | undefined’ is not assignable to type ‘boolean’.

>Solution :

You’re pretty close. 2 fixes:

1. Use T extends instead of T =
2. Index GameOptions by T

export class MyClass {
  get<T extends keyof GameOptions>(option: T): GameOptions[T] {
    return this.#options[option];
  }
}