title: Remove a property from an immutable JS object
body: <p>In my react-native application, I want to remove a property of my js object which is in redux. </p>
  
  <p>here is my code.</p>
  
  <pre><code>    case SAVE_PLAYLIST:
          const { toPlayListFrom, selectedPlaylist } = action.payload;
  
          let newPlaylists = // state.savedPlaylists;
              Object.keys(selectedPlaylist).length &gt; 0
                  ?  {
                      ...state.savedPlaylists,
                      [toPlayListFrom]: selectedPlaylist
                  }
                  : delete state.savedPlaylists[toPlayListFrom];
  
          return {
              ...state,
              savedPlaylists: newPlaylists
          }
  </code></pre>
  
  <p>in this line, <code>delete state.savedPlaylists[toPlayListFrom]</code> it doesn't remove the property as expected. How can I delete a property from an immutable js object in a right way?</p>