AsheKR/refactoring

First, you'll need to have a reasonably modern version of node handy. This won't work with versions older than 9, for instance.

Install the dependencies

$ npm install

Run the tests ✔️

$ npm test

 PASS  ./index.test.js
  ✓ throws invalid number (3ms)
  ✓ wait 500 ms (504ms)
  ✓ test runs (95ms)

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