# Defined

## `Defined<Type>`

A generic type `Defined` indicates the generic type variable [`Type`](#type) is never [`undefined`](https://www.typescriptlang.org/docs/handbook/basic-types.html#null-and-undefined). It takes generic type variable [`Type`](#type) constrained by [`undefined`](https://www.typescriptlang.org/docs/handbook/basic-types.html#null-and-undefined) which constraint causes its change to [`never`](https://www.typescriptlang.org/docs/handbook/basic-types.html#never).

{% code title="defined.type.ts" %}

```typescript
type Defined<Type> = Type extends undefined ? never : Type;
```

{% endcode %}

### Generic type variables

#### `Type`

A generic type variable `Type` is never [`undefined`](https://www.typescriptlang.org/docs/handbook/basic-types.html#null-and-undefined) but captured type.