JavaScript percentage calculation functions
Code level comments usually lose their context if not properly maintained. Using self descriptive variable names is a good choice. Appreciate your efforts in keeping the code highly readable.


First method, is trying to get the Percentage value, I would update the method definition to getPercentOfValue(from, percentage).
Second method, is trying to calculate percent rate, I would update the method definition to getPercentRate(newValue, originalValue) to follow the terminology in formula.