WIP Fix js exports issues

[mstoykov]

No description provided.

[codecov-io]

Codecov Report

Merging #1099 into master will decrease coverage by 0.03%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master    #1099      +/-   ##
==========================================
- Coverage   73.26%   73.22%   -0.04%     
==========================================
  Files         141      141              
  Lines       10251    10248       -3     
==========================================
- Hits         7510     7504       -6     
- Misses       2300     2302       +2     
- Partials      441      442       +1

Impacted Files	Coverage Δ
js/initcontext.go	89.88% <81.81%> (-3.6%)	⬇️

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[mstoykov]

After way more testing and banging of my head against a figurative wall, I managed to find out why the second fix works :) :

As is seen in that commit exports and module are being set to the goja.Runtime which basically sets them at the global scope. This was done before each import/require in order for subsequent exports/modules to not overwrite previous once. But after that the old ones are set back through the defers.

So that means that while during the execution of a module it sees it's exports/modules it sees the ones of the module that is entrypoint for the main function call. Usually(always in real k6 execution) this means the one of the main module - the one with the default function. Which is exactly what happens in the test - the function call to B during the execution of the main default function sees the exports/modules for the main script which are set at a different place.

When I changed it to instead have arguments to the function wrapper and provide the exports/module this way, they shadow the global ones and everything works as expected.

I suspect that the other fix works in some similar manner but also works around the fact that the main module's exports/module are still being set globally which I am going to test and change to work in the same way the import's ones work now.

[na--]

I've mostly grokked the changes here and don't see any issues so far...