Make javascript key optional

[alvinthen]

Close #569

[codecov]

Codecov Report

Merging #570 into master will decrease coverage by 0.06%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #570      +/-   ##
==========================================
- Coverage   84.76%   84.69%   -0.07%     
==========================================
  Files          48       48              
  Lines        4003     4006       +3     
  Branches      903      904       +1     
==========================================
  Hits         3393     3393              
- Misses        610      613       +3

Impacted Files	Coverage Δ
src/ParseFile.js	80% <0%> (-2.36%)	⬇️

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[flovilmart]

Thanks for the PR