Since i don't have enought rep to comment Im writing an answer.

• You might want to export the class and not the instance of the class. That might be causing an issue - the currentMonth and currentYear won't get reset either.
• You would also want to avoid creating conflicting class names like Date

// when exporting
module.exports = myDateClass


// when importing
const Date = require('./myDateClass')
const date = new Date()