TS2571

error TS2571: Object is of type ‘unknown’.

Broken Code ❌

If you use third-party libraries then it can happen that TypeScript cannot infer all return types. In such a case a return type can be unknown which makes it impossible to access its properties from TypeScript. In the following example such case is constructed by assigning unknown to an exemplary constant:

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const x: unknown = 1337;
console.log(x.toString());

Fixed Code ✔️

To solve the problem of accessing properties from an unknown object, we have to define the type of the object which we want to access:

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const x: number = 1337;
console.log(x.toString());

Broken Code ❌

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export const hasUsers = (payload: unknown): payload is {users: string[]} => {
  return 'users' in payload;
};

Fixed Code ✔️

If your variable is of type unknown, then you can use a type guard to narrow the type of your variable. If you want to be sure that you have an object at hand, you can use the typeof type guard:

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export const hasUsers = (payload: unknown): payload is {users: string[]} => {
  if (payload && typeof payload === 'object') {
    return 'users' in payload;
  }
  return false;
};

Alternative

You may also get the error “Object is of type ‘unknown’” when catching errors. In this case you have to type the error in your catch clause.