index.js

handleReturn = (event: SyntheticKeyboardEvent<*>) => {
  const { onSubmit } = this.props;
  
  if (event.shiftKey) return "not-handled";
  if (onSubmit) onSubmit();
  return "handled";
};

clear = () => {
  const { editorState: oldEditorState } = this.state;
  const oldContentState: ContentState = oldEditorState.getCurrentContent();
  const firstBlock: ContentBlock = oldContentState.getFirstBlock();
  const lastBlock: ContentBlock = oldContentState.getLastBlock();
  const selection: SelectionState = new SelectionState({
    anchorKey: firstBlock.getKey(),
    anchorOffset: 0,
    focusKey: lastBlock.getKey(),
    focusOffset: lastBlock.getLength(),
    hasFocus: true
  });
  const contentState: ContentState = Modifier.removeRange(
    oldContentState,
    selection,
    "backward"
  );
  const editorState: EditorState = EditorState.push(
    oldEditorState,
    contentState,
    "remove-range"
  );

  this.setState({
    editorState: EditorState.forceSelection(
      editorState,
      contentState.getSelectionAfter()
    )
  });
};