Extract keys of methods of TypeScript type

method-keys.ts

// https://www.typescriptlang.org/play/#code/C4TwDgpgBAshwAsD2ATA0hEBnA8gJwDkIA3CPAHgBUA+KAXigG8AoKNqAbTSgEsA7KAGtMSAGZRKAXQBcErpKgQAHsAh8UWKADEArnwDGwHkgEB+KN1l8SZANzMAvs1CRY8ZOkxYqtBnESoGNj4RKQUNBzCIGISkvbM-Kp4ogCG+tAAkkys7HxWOgC2AEZ2OWyiABQp+cVkAJSyWMB4-ADm9uxQrRUNUMRIPCj2Ti7QWvRuAZ7Y5BnUtmwA9ItQAESiq1AAPmutq8xAA
type MethodKeysOrNever<T> = {
    [K in keyof T]: T[K] extends Function ? K : never;
}
type MethodKeys<T> = MethodKeysOrNever<T>[keyof T];

MethodKeysOrNever transforms T into a class with value types equal either to the key (for method keys) or never. Now MethodKeys extracts the value types for all these keys. But never drops out of union types, leaving just the key types of T that map to a function type.