Javascript Date relativeDays()

/*** 16/10 - Patch not submitted yet ***/

// Returns the number of days since the Date
Date.prototype.relativeDays = function() {
 var now = new Date();
 var interval = now.getTime() - this.getTime();
 interval = Math.floor(interval / (1000 * 60 * 60 * 24));
 return interval;
};