Inference with const

Learn literal type inference with const.

Inference with const

With const, TypeScript infers a literal type, meaning the exact value becomes the type. In const x = 5, the type of x is not number but the literal type 5. This is because const variables cannot be reassigned.

const x = 5;          // type: 5
const y = "merhaba";   // type: "merhaba"

const uses a literal type because the value never changes.

let vs const inference difference

With let, TypeScript widens the type: let x = 5 gives type number. With const, the literal type is preserved: const x = 5 gives type 5. This difference arises because let variables can receive other values of the same type, while const never changes.

let a = 5;      // type: number
const b = 5;    // type: 5

let gives a wide type; const gives a narrow literal type.

Exercise Multiplication with const and let

Define a const named carpan with value 3. Define a let named deger with value 7. Print the result of carpan * deger with console.log.

Show example solution

const carpan = 3;
let deger = 7;
console.log(carpan * deger);

Test yourself

In <code>const renk = "kırmızı";</code>, what is the inferred type of <code>renk</code>?
- string (general type)
- const (keyword)
- "kırmızı" (literal type)
- renk (variable name)
Show answer

"kırmızı" (literal type) — Since <code>const</code> does not change, TypeScript infers the exact value as a literal type; the type of <code>renk</code> is <code>"kırmızı"</code>, not the general <code>string</code>.

Find the const literal type

const kod = 200;
// kod'un türü: ____

Show answer

const kod = 200;
// kod'un türü: 200

const inference concepts

const x = "a"

Literal type inference
let x = "a"

General type inference
const x = 5

Type: 5 (literal)
const inference

Produces exact value type

Next lesson: Best common type

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