site: add frontmatter parsing support

site/vite.config.ts

@@ -1,15 +1,32 @@
 import { sveltekit } from "@sveltejs/kit/vite";
 import { defineConfig } from "vite";
+import { matter } from "vfile-matter";
+import { unified } from "unified";
+import { VFile } from "vfile";
+import remarkParse from "remark-parse";
+import remarkRehype from "remark-rehype";
+import rehypeStringify from "rehype-stringify";
 
 export default defineConfig({
   plugins: [
     sveltekit(),
     {
       name: "markdown-loader",
-      transform(code, id) {
-        if (id.slice(-3) === ".md") {
-          return `export default ${JSON.stringify(code)};`;
-        }
+      async transform(code, id) {
+        if (id.slice(-3) !== ".md") return;
+
+        // TODO: move VFile into unified
+        const file = new VFile(code);
+        matter(file, { strip: true });
+        const html = await unified()
+          .use(remarkParse)
+          .use(remarkRehype)
+          .use(rehypeStringify)
+          .process(String(file));
+
+        return `
+export default ${JSON.stringify(String(html))};
+export const frontmatter = ${JSON.stringify(file.data.matter)};`;
       },
     },
   ],