Example code not working (happy and sad both NaN)

Hi there,

I checked out the code, ran "npm install", then "node index.js", but I get the following output:
```
{ happy: NaN, sad: NaN }
```
Any idea what's going wrong? I'm running on Windows, if that matters.

Start by running npm install and node index.js, then inspect index.js to trace why both reported values become NaN. Use the existing output as the reproduction case and determine what input or calculation produces the invalid values. Done means the example runs without NaN and reports numeric happy and sad values.

Written by the indexing model from the issue text.