tailwind-nextjs-blog/lib/remark-extract-frontmatter.ts

import { VFile } from 'vfile';
import { visit, Parent } from 'unist-util-visit';
import { load } from 'js-yaml';

export default function extractFrontmatter() {
  return (tree: Parent, file: VFile) => {
    visit(tree, 'yaml', (node: Parent) => {
      //@ts-ignore
      file.data.frontmatter = load(node.value);
    });
  };
}