Use TypeScript Conditional Types Like a Pro

util.d.ts

type FunctionPropertyNames<T> = {
    [K in keyof T]: T[K] extends Function ? K : never;
}[keyof T];
type FunctionProperties<T> = Pick<T, FunctionPropertyNames<T>>;
​
type NonFunctionPropertyNames<T> = {
    [K in keyof T]: T[K] extends Function ? never : K;
}[keyof T];
type NonFunctionProperties<T> = Pick<T, NonFunctionPropertyNames<T>>;
​
interface User {
    id: number;
    name: string;
    age: number;
    updateName(newName: string): void;
}
​
type T5 = FunctionPropertyNames<User>; // "updateName"
type T6 = FunctionProperties<User>; // { updateName: (newName: string) => void; }
type T7 = NonFunctionPropertyNames<User>; // "id" | "name" | "age"
type T8 = NonFunctionProperties<User>; // { id: number; name: string; age: number; }