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typescript

TS2571: Object is of type 'unknown'

You're trying to access a property or call a method on a value typed as unknown. Unlike any, unknown requires you to narrow the type first — TypeScript won't let you perform operations on unknown values without first confirming what they are.

Common causes

Catching an exception in a catch block — TypeScript types the caught error as unknown with useUnknownInCatchVariables
A function or API returns unknown and you're using the value without narrowing first
Receiving data from an external source typed as unknown to force explicit validation
A JSON.parse() result was typed as unknown for safety and isn't narrowed before use

How to fix it

Narrow with typeof: if (typeof value === 'string') { value.toUpperCase() }
Narrow with instanceof: if (error instanceof Error) { error.message }
For catch blocks: if (err instanceof Error) { console.log(err.message) } else { console.log(String(err)) }
Use a type guard function to validate and narrow the type before use

Example

try {
  riskyOperation();
} catch (err) {
  console.log(err.message);
  // error TS2571: Object is of type 'unknown'.
}

Accessing .message on the catch parameter, which is typed as unknown in strict mode

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