Make sure wrapper doesn't invalidate strict mode

[emilbroman-eqt]

The overridden module wrapper that decorates the require function adds an assignment statement before the module script itself. If that module starts with the "use strict" directive, that needs to be at the very top of the function to have any effect. The injected assignment invalidates that.

This led to a particularly weird bug initially reported to Axios here: axios/axios#3470

The solution is to wrap the module's script into another IIFE.

Note however that this changes the semantics in another way: it adds a stack frame to all modules. This could be an issue if someone is doing something funky with new Error().stack.

[emilbroman-eqt]

Please note that this can be considered severe, since it silently makes strict mode disabled for any module, first or third party, if it uses the module-wide directive. And strict/non-strict mode bugs are notoriously hard to troubleshoot. Trust me, this one was 😅

[mcollina]

good spot!

LGTM

[mcollina]

Unfortunately this does not pass on node v4. Would you mind updating .travis.yml dropping v4, v6, v8 and adding v12 and v14? Thanks

[codecov-io]

Codecov Report

Merging #29 (8c1ade9) into master (eccac78) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #29   +/-   ##
=======================================
  Coverage   98.00%   98.00%           
=======================================
  Files           2        2           
  Lines          50       50           
=======================================
  Hits           49       49           
  Misses          1        1           

Impacted Files	Coverage Δ
index.js	97.22% <100.00%> (ø)

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[mcollina]

lgtm