handlePaste.js

const fromHTML = convertFromHTML({...});

// within a wrapping component    
handlePastedText(text, html) {
  const {
    editorState,
    onChange
  } = this.props;

  const pastedContentState = fromHTML(html || text);

  const updatedContentState = Modifier.replaceWithFragment(
    editorState.getCurrentContent(),
    editorState.getSelection(),
    contentStateWithStyle.getBlockMap()
  );
  
  const updatedEditorState = EditorState.push(
    editorState,
    updatedContentState,
    'insert-fragment'
  );

  onChange(updatedEditorState);

  return true;
}