An error occurred when trying to access object references within a function

Here is a snippet of my code:

const fn1 = (param1: string, param2: string, param3: string): Promise<void> => {return new Promise()}

const fn2 = (param1: string, param2: string): void => {return}

const options = {
  option1: fn1,
  option2: fn2,
  option3: fn1,
  option4: fn2,
}

const myOption = 'option1';
const myParam1 = 'a';
const myParam2 = 'b';
const myParam3 = 'c';

options[myOption](myParam1, myParam2, myParam3); // ERROR in this line

I started with Javascript but then had to switch to TypeScript. The linter doesn't report any issues, however when I try to run it using ts-node, an error is displayed:

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type...[the type object here]

How do I properly type the object so that I can call the functions inside without resorting to a switch/case or endless else/if statements?

typescriptts-node

Answer №1

Perhaps not the ideal solution, but it did the trick:

const selections: Record<string, typeof action1 | typeof action2> = {
  selection1: action1,
  selection2: action2,
  selection3: action1,
  selection4: action2,
}

In TypeScript, the identifiers - selection1, selection2... are being recognized as enums rather than strings.

Answer №2

When running the code with ts-node, I haven't encountered this error. However, you may want to experiment by specifying the type of myOption as:

const myOption: keyof typeof options = 'option1';

Answer №3

In the case where `myOption` originates from a string array, you have the option to create a typeguard that ensures it is actually of type `keyof typeof options`. This specific type guarantees the correct indexing for your `options` object.

   function isKeyOfOptions(value: string): value is keyof typeof options {
      return options[value] !== undefined;
    }

    if(isKeyOfOptions(str))
       options[str](myParam1, myParam2, myParam3) 
       // Within this block, 'str' is constrained to "option1", "option2", "option3", or "option4";

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