fix: support classes

[lukeed]

Closes #4

[codecov-commenter]

Codecov Report

Merging #5 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master        #5   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines           12        16    +4     
=========================================
+ Hits            12        16    +4     

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

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