This is a minimal reproducer for a Chromium browser bug:
https://issues.chromium.org/issues/401652934

A variable is evaluated as NaN despite not being NaN.

While this reproducer assigns testVar the value 0 * Math.PI,
i've observed this bug in a different context i can't reproduce where a simple
timestamp was assigned to the variable afterwards being evaluated as NaN.

For this reproducer, using the multiplication of 0 and Math.PI or Math.E
seems necessary, i don't know why.

The function accessing testVar being in a different js source file was a
requirement to reproduce at least for me.

For more information, please read the source for a.js and b.js
Also check the development console output.

Update: setInterval context not necessary to reproduce