Sha256: 36c05e7b3586aefb636d84a555dbec0055c85d3955ff2c388656fb6a914d5830
Contents?: true
Size: 1.19 KB
Versions: 33
Compression:
Stored size: 1.19 KB
Contents
/**
Extract the keys from a type where the value type of the key extends the given `Condition`.
Internally this is used for the `ConditionalPick` and `ConditionalExcept` types.
@example
```
import {ConditionalKeys} from 'type-fest';
interface Example {
a: string;
b: string | number;
c?: string;
d: {};
}
type StringKeysOnly = ConditionalKeys<Example, string>;
//=> 'a'
```
To support partial types, make sure your `Condition` is a union of undefined (for example, `string | undefined`) as demonstrated below.
@example
```
type StringKeysAndUndefined = ConditionalKeys<Example, string | undefined>;
//=> 'a' | 'c'
```
@category Utilities
*/
export type ConditionalKeys<Base, Condition> = NonNullable<
// Wrap in `NonNullable` to strip away the `undefined` type from the produced union.
{
// Map through all the keys of the given base type.
[Key in keyof Base]:
// Pick only keys with types extending the given `Condition` type.
Base[Key] extends Condition
// Retain this key since the condition passes.
? Key
// Discard this key since the condition fails.
: never;
// Convert the produced object into a union type of the keys which passed the conditional test.
}[keyof Base]
>;
Version data entries
33 entries across 33 versions & 1 rubygems