unknown type

Learn safe type checking with unknown.

The unknown type

The unknown type, like any, accepts any value but requires you to check its type before using it. This provides flexibility while keeping type safety. You cannot access an unknown value without a type check.

let x: unknown = "merhaba";
if (typeof x === "string") {
  console.log(x.toUpperCase());  // "MERHABA"
}

unknown is used as a safe alternative to any.

Type guard

To use an unknown value, you narrow its type with a type guard. The most common type guard is the typeof operator. After narrowing, you can safely perform type-specific operations.

let deger: unknown = 42;
if (typeof deger === "number") {
  console.log(deger * 2);  // 84
}

A type guard converts unknown to a specific type and enables safe access.

Exercise Type guard with unknown

Declare a variable named girdi of type unknown with value "merhaba". Use typeof to check whether it is a string; if so, convert it to uppercase with toUpperCase and print it with console.log.

Show example solution

let girdi: unknown = "merhaba";
if (typeof girdi === "string") {
    console.log(girdi.toUpperCase());
}

Test yourself

What is the key difference between <code>unknown</code> and <code>any</code>?
- unknown is faster than any
- unknown allows no value assignments
- unknown requires type checking before use
- There is no difference between unknown and any
Show answer

unknown requires type checking before use — <code>unknown</code> accepts any value but requires a type check (type guard) before use; <code>any</code> has no such check and is therefore unsafe.

Add the type guard

let deger: unknown = "merhaba";
if (typeof deger === ____) { console.log(deger.toUpperCase()); }

Show answer

let deger: unknown = "merhaba";
if (typeof deger === "string") { console.log(deger.toUpperCase()); }

unknown concepts

unknown

Type check required before use
typeof x === "string"

Type guard
unknown vs any

unknown is safer
Tür koruyucu

Type narrowing operation

Next lesson: never type

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies