build-mod.deno

const appendReferenceTypes = async (path, name) => {
  const data = await Deno.readTextFile(path);

  const dataWithReferenceHeader = `/// <reference types="./${name.replace(
    ".js",
    ".d.ts",
  )}" />\n\n${data}`;

  await Deno.writeTextFile(path, dataWithReferenceHeader);
};

const findSrcFilesAndAppendReferenceTypes = async dir => {
  for await (const dirEntry of Deno.readDir(dir)) {
    const path = dir + "/" + dirEntry.name;

    if (dirEntry.isFile && dirEntry.name.endsWith(".js")) {
      await appendReferenceTypes(path, dirEntry.name);
    } else if (dirEntry.isDirectory) {
      await findSrcFilesAndAppendReferenceTypes(path);
    }
  }
};

const srcDir = "./mod";
await findSrcFilesAndAppendReferenceTypes(srcDir);