How to use the @sveltejs/site-kit/utils/markdown.js.extract_frontmatter function in @sveltejs/site-kit

.map(file => {
			if (path.extname(file) !== '.md') return;

			const match = /^(\d+-\d+-\d+)-(.+)\.md$/.exec(file);
			if (!match) throw new Error(`Invalid filename '${file}'`);

			const [, pubdate, slug] = match;

			const markdown = fs.readFileSync(`content/blog/${file}`, 'utf-8');

			const { content, metadata } = extract_frontmatter(markdown);

			const date = new Date(`${pubdate} EDT`); // cheeky hack
			metadata.pubdate = pubdate;
			metadata.dateString = date.toDateString();

			const renderer = new marked.Renderer();

			renderer.link = link_renderer;

			renderer.code = highlight;

			renderer.heading = (text, level, rawtext) => {
				const fragment = makeSlug(rawtext);

				return `

.map(file => {
			const markdown = fs.readFileSync(`content/${dir}/${file}`, 'utf-8');

			const { content, metadata } = extract_frontmatter(markdown);

			const section_slug = make_slug(metadata.title);

			const subsections = [];

			const renderer = new marked.Renderer();

			let block_open = false;

			renderer.link = link_renderer;

			renderer.hr = () => {
				block_open = true;

				return '<div class="side-by-side"><div class="copy">';
			};</div></div>

.map(file => {
			const markdown = fs.readFileSync(`content/docs/${file}`, 'utf-8');

			const { content, metadata } = extract_frontmatter(markdown);

			const section_slug = make_slug(metadata.title);

			const subsections = [];

			const renderer = new marked.Renderer();

			let block_open = false;

			renderer.link = link_renderer;

			renderer.hr = () => {
				block_open = true;

				return '<div class="side-by-side"><div class="copy">';
			};</div></div>