Fix IE9 console issue

[laysent]

This is a similar commit trying to solve IE9 console issue addressed once by #185
Also, the other commit fix a lint issue introduced by #205

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@539dab5). Click here to learn what that means.
The diff coverage is 0%.

@@           Coverage Diff           @@
##             master   #259   +/-   ##
=======================================
  Coverage          ?    82%           
=======================================
  Files             ?      5           
  Lines             ?    150           
  Branches          ?      0           
=======================================
  Hits              ?    123           
  Misses            ?     27           
  Partials          ?      0

Impacted Files	Coverage Δ
src/defaults.js	75% <ø> (ø)
src/core.js	73.33% <0%> (ø)

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