Type alias FilterBy<T, P>

FilterBy<T, P> filters keys from the object type T based on a specified predicate P.

Remark

This type performs a shallow filtering of keys within T and does not check deeply nested types or complex structures within the object type.

It does not return the key as a whole object, it just returns the key itself

Example

type T = {
  a: () => 1;
  x: string;
  s: {
    q: Nullable;
    s: {
      i: {
        x: {
          o: boolean;
          n: Falsy;
        };
        e: 'foo';
      };
    };
  };
};

Copy

type _ = FilterBy<T, 'a'>
Copy

Results in the type 'a', which includes only the key 'a' from T.

type _ = FilterBy<T, Falsy>
Copy

Results in the type never, indicating that no keys in T match the type Falsy.

type _ = FilterBy<T, string>
Copy

Results in the type 'a' | 'x' | 's', which includes all top-level keys of T that are of type string. It did not pick up on 'e' as it is nested down.