export.js

const INTERNAL_PROPS = new Set([
  '__first',
  '__last',
  '__size',
  '__parent',
  '__next',
  '__prev',
  '__cachedText',
  '__key',
]);

exportJSON() {
  const serializedNode: {[key: string]: unknown} = {type: this.getType()};
  const node = this.getLatest();
  const isTextNode = $isTextNode(this);
  const isElementNode = $isElementNode(this);

  for (const key in Object.keys(node)) {
    if (
      key[0] !== '_' ||
      key[1] !== '_' ||
      INTERNAL_PROPS.has(key) ||
      (isElementNode && (key === 'children' || key === '__format')) ||
      (isTextNode && key === '__mode')
    ) {
      continue;
    }

    let value = node[key as keyof LexicalNode];

    if (value instanceof LexicalEditor) {
      // @ts-ignore better typing?
      value = value.toJSON();
    }

    serializedNode[key.slice(2)] = value;
  }

  if (isElementNode) {
    serializedNode.children = [];
    // @ts-ignore wish type predicates worked here
    serializedNode.format = this.getFormatType();
  } else if (isTextNode) {
    // @ts-ignore wish type predicates worked here
    serializedNode.mode = this.getMode();
  }

  return serializedNode;
}