a-yaml-loader.mjs

import { fileURLToPath } from "url";
export async function load(url, context, defaultLoad) {
    if(/\.yaml$/.test(url)) {
        const path = fileURLToPath(new URL(url));
        return {
            format: "module",
            source: `
import fs from "fs/promises";
import YAML from 'yaml';
const yamlSource = await fs.readFile(${JSON.stringify(path)}, "utf8");
export default YAML.parse(yamlSource);
            `
        }
    }

    // Defer to Node.js for all other URLs.
    return defaultLoad(url, context, defaultLoad);
}

package.json

{
  "name": "yaml-loader",
  "exports": {
    ".": "./a-yaml-loader.mjs"
  }
}