¿Alguien puede explicar cómo funciona la lógica en monthDiff de moment.js? Aquí está el extracto de la función diff.

 function monthDiff(a, b) { if (a.date() < b.date()) { // end-of-month calculations work correct when the start month has more // days than the end month. return -monthDiff(b, a); } // !!! I DON'T UNDERSTAND FROM HERE BELOW !!! // difference in months var wholeMonthDiff = (b.year() - a.year()) * 12 + (b.month() - a.month()), // b is in (anchor - 1 month, anchor + 1 month) => Why? Any theory or Math formula? anchor = a.clone().add(wholeMonthDiff, 'months'), anchor2, adjust; if (b - anchor < 0) { anchor2 = a.clone().add(wholeMonthDiff - 1, 'months'); // linear across the month adjust = (b - anchor) / (anchor - anchor2); } else { anchor2 = a.clone().add(wholeMonthDiff + 1, 'months'); // linear across the month adjust = (b - anchor) / (anchor2 - anchor); } //check for negative zero, return zero if negative zero return -(wholeMonthDiff + adjust) || 0; }

Referencia: https://github.com/moment/moment/blob/develop/src/lib/moment/diff.js