TS2538

error TS2538: Type ‘Person’ cannot be used as an index type.

Broken Code ❌

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interface Person {
  name: string;
}

function getValue(person: Person, key: Person): string {
  return person[key];
}

Fixed Code ✔️

You cannot use an interface as an index type, but you can use all keys of the interface using the keyof type operator:

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interface Person {
  name: string;
}

function getValue(person: Person, key: keyof Person): string {
  return person[key];
}