• list
• reply
• write

TypeScript unknown Type

The unknown type in TypeScript is used when you want to accept any value, but require type checking before using it. It is safer than any because TypeScript forces you to verify the type before performing operations.

Basic Usage

let value: unknown;

value = "hello";   // OK
value = 42;        // OK
value = true;      // OK

Unsafe Access

let value: unknown = "hello";
console.log(value.toUpperCase()); // Error: Object is of type 'unknown'

Safe Access with Type Checking

if (typeof value === "string") {
  console.log(value.toUpperCase()); // OK
}

Type Assertion

console.log((value as string).toUpperCase()); // OK

Comparison: unknown vs any

When to Use unknown

• Handling external data (e.g., API responses)
• Processing user input
• As a safer alternative to any