Validated values
Define a field or result that must contain a concrete value after validation.
TypeScript · Type Alias
NonNullable
NonNullable<Type> removes null and undefined from a type. It is useful for describing values that remain after nullish cases have been ruled out.
- Since
- 2.8
How it works
NonNullable<Type> transforms a type by removing null and undefined from it. Applied to a union, it preserves the remaining members, making it useful for representing values after validation or other checks.
Syntax
type NonNullable<Type> = Type & {};Parameters
| Name | Type | Description |
|---|---|---|
Type | type | The input type from which null and undefined are excluded. |
Returns
A type derived from Type with null and undefined excluded.
Key points
- NonNullable<Type> creates a version of Type without null or undefined.
- For string | number | undefined, the resulting type is string | number.
- For string[] | null | undefined, the resulting type is string[].
Common mistakes
- NonNullable is built into TypeScript and does not need to be imported.
- It only excludes null and undefined; other union members remain unchanged.
Example: Removing null and undefined from a value
type Present<T> = NonNullable<T>;
function requireValue<T>(value: T): NonNullable<T> {
if (value == null) throw new Error("Missing value");
return value as NonNullable<T>;
}
const name: string | undefined = "Ada";
const presentName = requireValue(name);
console.log(presentName.toUpperCase());This runnable example removes nullish possibilities from a generic result after a runtime check.
When to use it
API and configuration modeling
Derive a non-nullable type from an API or configuration union.
Generic helpers
Express generic return types after rejecting nullish inputs.
Related
ExcludeRequiredstrictNullChecksUtility Types