Adds additional check functionalitiy to Date Object

Date.js

/*    Adds isAfter, isBefore, and isBetween functions to the Date object
*     isAfter(<Date Object>) OR isAfter('MM/DD/YYYY')
*     isBefore(<Date Object>) OR isBefore('MM/DD/YYYY')
*     isBetween(<Start Date Object>, <End Date Object>) OR isBetween('MM/DD/YYYY','MM/DD/YYYY')
*
*     Assuming todays' date is 12/25/2018
*     var date = new Date(); 
*     date.isAfter('12/12/2018') returns true;
*     date.isBefore('12/12/2018') returns false;
*     date.isBetween('12/1/2018','12/31/2018') returns true;
*/

Date.prototype.isAfter = function(date){
	var today = this;
	switch (typeof date){
		case 'object':
			date = date;
			break;
		case 'string':
			date = Date.parse(date);
			break;
	}
	// check for bad date in case 'string':
	if(date.toString() === 'NaN'){
		console.error('Parameter must be properly formatted Dates:\neither Date() objects or text "MM/DD/YYYY"');
		return;
	}
	if(today > date){
		return true;
	}
	else{
		return false;
	}
}
Date.prototype.isBefore = function(date){
	var today = this;
	switch (typeof date){
		case 'object':
			date = date;
			break;
		case 'string':
			date = Date.parse(date);
			break;
	}
	// check for bad date in case 'string':
	if(date.toString() === 'NaN'){
		console.error('Parameter must be properly formatted Dates:\neither Date() objects or text "MM/DD/YYYY"');
		return;
	}
	if(today < date){
		return true;
	}
	else{
		return false;
	}
}
Date.prototype.isBetween = function(start, end){
	var today = this;
	var NaN = false;
	switch(typeof start){
		case 'object':
			start = start;
			break;
		case 'string':
			start = Date.parse(start);
			break;
	}
	switch(typeof end){
		case 'object':
			end = end;
			break;
		case 'string':
			end = Date.parse(end);
			break;
	}
	// check for bad dates in case 'string':
	if(start.toString() === 'NaN' || end.toString() === 'NaN'){
		console.error('Parameters must be properly formatted Dates:\neither Date() objects or text "MM/DD/YYYY"');
		return;
	}
	// check start/end logic
	if(start > end){
		console.error('Start date must be before End date');
		return;
	}

	if(today >= start && today <= end && start < end){
		return true;
	}
	else{
		return false;
	}
}