`import` a module without caching it

uncachedImport.js

import fs from "fs/promises";
import url from "url";
import vm from "vm";

/**
 * Import a single module without caching it; if you call this function again the module will be re-imported
 * 
 * Moderately leaky workaround for https://github.com/nodejs/modules/issues/307
 *
 * Note:
 *  * Requires --experimental-vm-modules --experimental-import-meta-resolve
 *  * Has a memory leak due to https://github.com/nodejs/node/issues/33439 (and possibly also V8?), but is
 *    less leaky than this workaround: https://github.com/nodejs/modules/issues/307#issuecomment-764560656
 *    Tested both approaches importing a ~2.5MB module hundreds of times, memory grew at half the rate
 *  * Dependencies are imported normally, so those do not get re-imported
 *  * Could be sped up with createCachedData, at the expense of greater memory usage
 */
export async function uncachedImport(specifier) {
  const moduleUrl = await import.meta.resolve(specifier);
  return vm.runInThisContext(`import(\"${specifier}\");`, {
    async importModuleDynamically() {
      const module = new vm.SourceTextModule(await fs.readFile(url.fileURLToPath(moduleUrl), "utf-8"), {
        importModuleDynamically: realImport,
        initializeImportMeta(meta) {
          meta.url = moduleUrl;
        },
      });
      await module.link(realImport);
      await module.evaluate();
      return module;
    },
  });
}

const _cache = new Map();
// need to wrap real sub-imports in a vm.Module
async function realImport(specifier) {
  if (_cache.has(specifier)) {
    return _cache.get(specifier);
  }

  const mod = await import(specifier);
  const result = new vm.SyntheticModule(Object.keys(mod), function () {
    Object.entries(mod).forEach(([key, value]) => {
      this.setExport(key, value);
    });
  });
  _cache.set(specifier, result);
  return result;
}