usestate-complex.tsx

import * as React from 'react';

interface IUser {
  username: string;
  email:  string;
  password: string;
}

const ComplexState = ({ initialUserData }) => {
  const [user, setUser] = React.useState<IUser | null>(initialUserData);
  
  if (!user) {
    // do something else when our user is null
  }

  return (
    <form>
      <input value={user.username} onChange={e => setUser({...user, username: e.target.value})} />
      <input value={user.email} onChange={e => setUser({...user, email: e.target.value})} />
      <input value={user.password} onChange={e => setUser({...user, password: e.target.value})} />
    </form>  
  );
}

Typo?
React.userState -> React.useState