Cannot return value from a SourceTextModule to the caller

[clecap]

• Version: v15.9.0
• Platform: macOS Catalina 10.15.6
• Subsystem: VM

What steps will reproduce the bug?

Make file retu.js.

const vm = require('vm');
const contextifiedSandbox = vm.createContext({ });
(async () => {
  const bar = new vm.SourceTextModule(`19;`, { context: contextifiedSandbox });
  async function linker(specifier, referencingModule) { }
  await bar.link(linker);
  const  result  = await bar.evaluate();
  console.log("Result is: ", result);
})();

Run as node --experimental.vm.modules retu.js

What is the expected behavior?

According to the current state of the documentation I expect an output of Result is: 19

What do you see instead?

Output of: Result is: undefined

[devsnek]

This is working as intended. Can you point me to the location in the docs where it suggests otherwise?

[clecap]

It pretty much is possible that I misunderstood the docs. What I found was in https://nodejs.org/dist/latest-v15.x/docs/api/vm.html#vm_module_evaluate_options the information that evaluate should return a Promise (but the docs there do not provide a hint as to how that value is derived and to which value the promise should resolve). My naive expectation is that the value of a module is the value of the last expression in the module, which should be 19. This is the usual convention in several other, similar cases.

Seems I am not the only one with that problem: A similar question on https://www.titanwolf.org/Network/q/6b88da95-c21a-46dd-bc37-100842de1151/y is still unanswered and the 0.5 line answer in https://stackoverflow.com/questions/60796382/how-to-get-default-export-out-of-vm-sourcetextmodule I admit I do not understand.

So the issue might as well be an issue with the docs (or with my ability to understand the docs).

[devsnek]

I think the fix here would be to change the docs to say Returns: <Promise> Fulfills with undefined upon success. Would you like to do so? If not I will get around to it eventually.

[clecap]

What then would be the way to obtain a value from a module and, for example, access a default export?

Wrt a PR on the doc: I am not so knowledgable on how to do that in github :(

[devsnek]

@clecap the default export is available via module.namespace.default, though it would be undefined in your example. There is no way to access the "last evaluated expression" as there is with vm.Script.