allow some js lose

[xieyiwen]

#179

[codecov-io]

Codecov Report

Merging #181 into dev will decrease coverage by 0.03%.
The diff coverage is 71.42%.

@@            Coverage Diff             @@
##              dev     #181      +/-   ##
==========================================
- Coverage   92.42%   92.38%   -0.04%     
==========================================
  Files          48       48              
  Lines        7075     7079       +4     
==========================================
+ Hits         6539     6540       +1     
- Misses        536      539       +3

Impacted Files	Coverage Δ
pyppeteer/page.py	86.6% <71.42%> (-0.22%)	⬇️
pyppeteer/helper.py	89.32% <0%> (-3.89%)	⬇️
pyppeteer/execution_context.py	93.28% <0%> (+0.74%)	⬆️
pyppeteer/launcher.py	89.06% <0%> (+1.04%)	⬆️

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