[Draft.js plugins] How to force block style on first line for a heading/title like Medium

index.js

// Import and add to your Editor's plugins

import { RichUtils } from 'draft-js';

const HEADING = 'header-one';

export default () => ({
  onChange: (editorState) => {
    const currentContent = editorState.getCurrentContent();
    const firstBlockKey = currentContent.getBlockMap().first().getKey();
    const currentBlockKey = editorState.getSelection().getAnchorKey();
    const isFirstBlock = (currentBlockKey === firstBlockKey);
    const currentBlockType = RichUtils.getCurrentBlockType(editorState);
    const isHeading = currentBlockType === HEADING;
    if (isFirstBlock !== isHeading) {
      return RichUtils.toggleBlockType(editorState, HEADING);
    }
    return editorState;
  },
});