[Robustness] `stringify`: avoid relying on a global `undefined`

[Connormiha]

I just removed needless(for these cases) typeof for checking for undefined

update: Added checking for typeof in parser.

[Connormiha]

@ljharb

These are not needless at all. undefined can be redefined in every scope except the global scope in ES5, and in ES3 - which this package supports - it can be modified in the global scope otherwise.

Yes, but there are many places with same check. For example https://github.com/ljharb/qs/blob/master/lib/stringify.js#L155 or https://github.com/ljharb/qs/blob/master/lib/stringify.js#L195

[ljharb]

In that case, those should be changed to use typeof instead :-) want to update the PR to do that?

[Connormiha]

@ljharb typeof or void 0? Which one is preferable?

[Connormiha]

@ljharb updated.

[ljharb]

Definitely the typeof, because it has minimal runtime weight.

[codecov[bot]]

Codecov Report

Merging #427 (0a1d3e8) into master (408ff95) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #427   +/-   ##
=======================================
  Coverage   99.85%   99.85%           
=======================================
  Files           8        8           
  Lines        1408     1408           
  Branches      172      172           
=======================================
  Hits         1406     1406           
  Misses          2        2           

Impacted Files	Coverage Δ
lib/stringify.js	100.00% <100.00%> (ø)

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