Convert MDX with Frontmatter to MDX with Exports

// node fs comes with promises now
const fs = require("fs").promises;
// front-matter is what we used in gatsby-plugin-mdx to parse out frontmatter
const fm = require("front-matter");

const dir = "./a-directory";

// node doesn't allow top-level async/await yet, so we make it a function
// and then call it
async function run() {
  // read the filenames in the relevant directory.
  const files = await fs.readdir(dir, "utf-8");
  //
  await Promise.all(
    files
      .filter(name => name.endsWith("mdx"))
      .map(async filename => {
        // if we don't use `utf-8` we get a buffer
        const file = await fs.readFile(`${dir}/${filename}`, "utf-8");

        // attributes are the json representation of the frontmatter
        // body is everything else
        const { attributes, body } = fm(file);

        // grab the json representation of the frontmatter and export it
        // as the identifier meta
        const content = `export const meta = ${JSON.stringify(
          attributes,
          null,
          2
        )}
        
${body}`;

        // write the file back out
        await fs.writeFile(`${dir}/${filename}`, content, "utf-8");
       // return content but it doesn't matter because we don't use it
        return content;
      })
  );
}

run();