TypeScript provide alternative types while using keyof

I want to have a type that when specifying a specific key as the value to the property answerMethod (e.g. answerMethod: 'options') it should require an additional field (e.g. a string array with options)

Here is a non-working attempt at what I’ve been wanting to achieve:

const formComponents = {
  text: TextInput,
  options: Radio,
}

interface AnswerBase {
  name: string
  label: string
  helpText?: string
  value?: string
}

interface AnswerWithoutOptions extends AnswerBase {
  answerMethod: Omit<keyof typeof formComponents, 'options'>
}

interface AnswerWithOptions extends AnswerBase {
  answerMethod: 'options'
  options: string[]
}

type Answer = AnswerWithoutOptions | AnswerWithOptions

const answer: Answer = {
  name: 'title',
  label: 'Title',
  helpText: 'The title of the video.',
  answerMethod: 'notavalidmethod', // Expected an error.
  value: '',
}

The above code only allows the field options: string[] when answerMethod: 'options', but it doesn’t restrict answerMethod to be a key of formComponents and allows any string. answerMethod should only allow keys of formComponents.

Any guidance would be appreciated.

>Solution :

You want Exclude, not Omit. Omit is for removing keys from a type. It’s Exclude that excludes members from a union.

interface AnswerWithoutOptions extends AnswerBase {
    answerMethod: Exclude<keyof typeof formComponents, "options">;
// −−−−−−−−−−−−−−−^^^^^^^
}

Playground link