react map array state update code example

Example 1: how to update array in react state

this.setState(prevState => ({
  arrayvar: [...prevState.arrayvar, newelement]
}))

Example 2: new Map() collection in react state

function MapComponent(){
  const [myMap, setMyMap] = useState(new Map());
  const updateMap = (k,v) => {
    setMyMap(new Map(myMap.set(k,v)));
  }
  return(
    <ul>
      {[...myMap.keys()].map(k => (
        <li key={k}>myMap.get(k)</li>
      ))}
    </ul>
  );
}