Array element type

Learn to extract the element type of an array with infer.

Array element type

The pattern (infer E)[] extracts the element type of an array as E. The pattern T extends (infer E)[] ? E : never gives the element type when T is an array. This is useful in generic helpers that need to know an array's element type.

type Eleman<T> =
  T extends (infer E)[] ? E : never;
type R = Eleman<string[]>;
// R: string

Why the parentheses matter

In (infer E)[] the parentheses are mandatory. Writing infer E[] tries to declare an array of element types named E and is a syntax error. The parentheses say: first infer E, then require the type to be an array of E.

Exercise Extract the array element type

Write the conditional type Eleman<T> as T extends (infer E)[] ? E : never. Define type Sonuc as Eleman<string[]>. Define variable a with type Sonuc and assign "elma". Print a with console.log.

Show example solution

type Eleman<T> = T extends (infer E)[] ? E : never;
type Sonuc = Eleman<string[]>;
const a: Sonuc = "elma";
console.log(a);

Test yourself

What does Eleman<number[]> produce?
```
type Eleman<T> = T extends (infer E)[] ? E : never;
type R = Eleman<number[]>;
```
- number
- never
- any[]
- number[]
Show answer

number — Since T is an array, the pattern matches and E becomes the element type, number. The true branch returns E. number[] is the matched type itself; never is the wrong branch; any[] is not an inference result.

Add the array brackets

type Eleman<T> =
  T extends (infer E)____ ? E : never;

Show answer

type Eleman<T> =
  T extends (infer E)[] ? E : never;

Array infer parts

(infer E)

Inferred element type
(infer E)[]

Array match pattern
? E

True branch: the element type
Eleman<string[]>

Usage example

Next lesson: Summary - infer

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