// comprueba si el email es correcto
String.prototype.isEmail = function(){	
	
	if (this.length < 5)	{	return false;	}	
	var iChars = "*|,\":<>[]{}`';()&$#% ";
	var eLength = this.length;	
	for (var i=0; i < eLength; i++)	
	{		
		if (iChars.indexOf(this.charAt(i)) != -1)		
		{			
			return false;		
		}	
	}	
	var atIndex = this.lastIndexOf("@");	
	if(atIndex < 1 || (atIndex == eLength - 1))	{		
		return false;	
	}
	
	var pIndex = this.lastIndexOf(".");	
	if(pIndex < 4 || (pIndex == eLength - 1))	
	{		
		return false;	
	}	
	if(atIndex > pIndex)	{		
		return false;	
	}	
	return true;
}