JS modernised and tests added

[ppfeufer]

Description

Added

• Test suite

Changed

• JavaScript modernised

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have checked my code and corrected any misspellings

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@e29e55a). Click here to learn what that means. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #44   +/-   ##
=========================================
  Coverage          ?   81.48%           
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  Files             ?        9           
  Lines             ?      108           
  Branches          ?        5           
=========================================
  Hits              ?       88           
  Misses            ?       19           
  Partials          ?        1           

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