Why is it not possible to require() ES modules from CommonJS modules?

[kimamula]

• Node.js Version: v13
• OS: any
• Scope (install, code, runtime, meta, other?): other
• Module (and version) (if relevant): ECMAScript modules

Using dual package which exports both CommonJS and ES modules can be problematic as described.

If CommonJS modules could require() ES modules, both CommonJS modules and ES modules could always use the same ES modules in dual package and the problem should not occur.
I would like to know the reason why this is not possible.

[devsnek]

esm is asynchronous, which means require would have to return a promise. At that point, you should just use import().

[kimamula]

Thank you so much for the explanation.
That makes sense.

However, I can not find any description in the ECMAScript specification which says "esm is asynchronous".
Is it specified in any standard or only specific to Node.js?

[devsnek]

in the current specification you could technically resolve, link, and execute the entire graph synchronously. however, there is a stage 3 proposal called top level await which does force the graph loading to be async.

[kimamula]

Thanks for navigating me to top-level await!
I read here and here and understood why it's not possible for CommonJS modules to require() ES Modules!