() => void' is not assignable to type '() => {} code example

Example 1: Type 'Promise' is not assignable to type 'void | (() => void)'.

useEffect(() => {
  const genRandomKey = async () => {
    console.log(await ecc.randomKey())
  };

  genRandomKey();
}, []);

Example 2: 'this' context of type 'void' is not assignable to method's 'this' of type 'Observable<{}>'.

import { map } from "rxjs/operators";