testing https://stackoverflow.com/a/55479659/2410656

gistfile1.txt

// see https://repl.it/repls/AnimatedPerfectMinimalsystem
// 1 Transform the type to flag all the undesired keys as 'never'
type FlagExcludedType<Base, Type> = { [Key in keyof Base]: Base[Key] extends Type ? never : Key };

// 2 Get the keys that are not flagged as 'never'
type AllowedNames<Base, Type> = FlagExcludedType<Base, Type>[keyof Base];

// 3 Use this with a simple Pick to get the right interface, excluding the undesired type
type OmitType<Base, Type> = Pick<Base, AllowedNames<Base, Type>>;

// 4 Exclude the Function type to only get properties
type ConstructorType<T> = OmitType<T, Function>;

interface X {
    duration_msec: number;
    available(now: number): boolean;
}

let x:ConstructorType<X> = {
  duration_msec: 2,
};
let y:X = {
  ...x,
  available(now: number): boolean { return false; }
}
console.log("x", x);
console.log("y", y);