let message = [];
if ("message" in messageRenderer) {
    message = messageRenderer.message.runs;
}
else if ("headerSubtext" in messageRenderer) {
    message = messageRenderer.headerSubtext.runs;
}

{
  id: 'id',
  timestampUsec: '1673550636512193',
  authorExternalChannelId: 'channelId',
  headerPrimaryText: { runs: [ { text: 'Member for ' }, { text: '14' }, { text: ' months' } ] },
  headerSubtext: { simpleText: 'membership tier name' },
  
  empty: true,
  
  // メッセージがある場合、emptyキーは消え代わりにmessageキーがこのように出力されると思われる (#78 より)
  // "message": { "runs": [ { "text": "Hi" } ] },
  
  authorName: { simpleText: 'channel name' },
  authorPhoto: { thumbnails: [ [Object], [Object] ] },
  authorBadges: [
    { liveChatAuthorBadgeRenderer: [Object] },
    { liveChatAuthorBadgeRenderer: [Object] }
  ],
  contextMenuEndpoint: {
    clickTrackingParams: 'clickTrackingParams',
    commandMetadata: { webCommandMetadata: [Object] },
    liveChatItemContextMenuEndpoint: {
      params: 'params'
    }
  },
  contextMenuAccessibility: { accessibilityData: { label: 'Chat actions' } },
  trackingParams: 'trackingParams'
}