javascript - An index signature parameter type cannot be a union type. Consider using a mapped object type instead

Question

I'm trying to use the following pattern:

enum Option {
  ONE = 'one',
  TWO = 'two',
  THREE = 'three'
}

interface OptionRequirement {
  someBool: boolean;
  someString: string;
}

interface OptionRequirements {
  [key: Option]: OptionRequirement;
}

This seems very straightforward to me, however I get the following error:

An index signature parameter type cannot be a union type. Consider using a mapped object type instead.

What am I doing wrong?

Answer 1

You can use TS "in" operator and do this:

enum Options {
  ONE = 'one',
  TWO = 'two',
  THREE = 'three',
}
interface OptionRequirement {
  someBool: boolean;
  someString: string;
}
type OptionRequirements = {
  [key in Options]: OptionRequirement; // Note that "key in".
}