class A{
 someProp: String
 someMethod(){}
}

class B implements classA{
  someProp: String
  someMethod: () => void;
}

class B implements Partial<classA>{}

type Constructor<T = {}> = new (...args: any[]) => T;

function A<C extends Constructor>(Base: C) {
  return class extends Base {
    someProp: String
    someMethod(){}
  }

class B extends A(class {}) {}

class B {}
interface B extends A {}
Object.assign(B.prototype, A.prototype); // copy methods at runtime