Important feature: Allow busting ESM cache

[izelnakri]

Currently ESM modules are cached separately for ESM imports and dynamic imports. https://nodejs.org/dist/latest-v16.x/docs/api/esm.html#esm_no_require_cache

There is currently no way to remove the ESM cache for specific files/modules in node.js/JavaScript context. I"m 100% sure about this unless there is some weird undocumented way. I even tried the following to bust the cache and it doesnt work:

import { createRequire } from 'module';

export function runTests(testFiles) {
  const require = createRequire(import.meta.url); // NOTE: Here I'm creating `require` reference on ES module

  // ....

  Object.keys(require.cache).forEach((module) => delete require.cache[module]); // This clears the cache object but its not used by ESM
  
   // Then import the test modules directly serves cache
}

This missing feature prevents writing ESM based javascript test runners because test files need to be re-evaluated without cache on file changes. In other words, cache busting for ESM modules is an important feature that node.js should provide somehow.

[benjamingr]

@nodejs/modules

[devsnek]

this is a duplicate but I can't find the other issue on my phone. tldr is either append some sort of unique id to the url each time you want to import it (foo.mjs?v=1) or bug v8 about getting proper hot reloading support.

[izelnakri]

Would be great if we document foo.mjs?v=1 behavior in the API docs, will try it out today. Thanks!

[giltayar]

As usual, here's a link to my article on implementing mocking modules, which use the above technique: https://dev.to/giltayar/mock-all-you-want-supporting-es-modules-in-the-testdouble-js-mocking-library-3gh1

[izelnakri]

This works, thank you @devsnek and @giltayar , we should really document this in the API docs: https://nodejs.org/api/esm.html#esm_no_require_cache . Closing this issue now

[icetbr]

This landed on node 22: --experimental-require-module. It allows mocha --watch to work with ESM modules, which was broken feature due to require.cache. Maybe it can help you out.

Here is the person who found the "fix"
https://joyeecheung.github.io/blog/2024/03/18/require-esm-in-node-js/

The docs
https://nodejs.org/api/modules.html#loading-ecmascript-modules-using-require

Here is where I first saw the merge
#51977 (comment)