Now() Value in Coldfusion - coldfusion

Question

I am trying to set the expression #Now() + CreateTimeSpan('30','0','0','0')# in a cookie and manipulating the values in a JS function.
The value of the expression is being displayed as 41720.406? What does this value mean?
Any pointers would be really helpful.

Answer 1

41720.406? What does this value mean?
To answer your question, apparently it represents a number of days from the CF epoch ie 1899-12-30, plus or minus time zone offsets.
<cfscript>
cfEpoch = createDate(1899, 12, 30);
// add number of whole days ie 41720
finalDate = dateAdd("d", 41720, cfEpoch );
// add partial days ie partialDay * millisecondsPerDay
finalDate = dateAdd("l", 0.406 * 86400000, finalDate);
// Result: Today's date and time plus 30 days
writeOutput( "finalDate="& dateConvert("local2UTC", finalDate) );
</cfscript>
Having said that, it is much simpler to use date functions as others suggested, rather than mucking with time span objects.

Answer 2

You may want to use DateAdd() instead. So use DateAdd('d', 30, Now()).
<cfset x = DateAdd('d', 30, now())>
<cfoutput>#toScript(x, "time")#</cfoutput>
output:
time = new Date(2014, 2, 22, 2, 36, 26);

Answer 3

Since you mentioned cookies, it's worth pointing out that dates for cookies use a specific format, i.e. Thu, 01-Jan-1970 00:00:01 GMT
This is not how CF formats dates by default - when you output #SomeDate# the format used is {ts '1970-01-01 00:00:01'} instead.
Here's a function that returns a date as a string in the format cookies use:
<cffunction name="formatCookieDate" returntype="String" output=false access="public">
<cfargument name="DateTime" type="Date" default=#Now()# />
<cfargument name="isUtc" type="String" default=false />
<cfif NOT Arguments.isUtc >
<cfset Arguments.DateTime = DateConvert('local2utc',Arguments.DateTime) />
</cfif>
<cfreturn DateTimeFormat( Arguments.DateTime ,'E, dd Mmm yyyy HH:nn:ss' ) & ' GMT' />
</cffunction>
You can use it like this:
formatCookieDate( Now() + 30 )
Whilst some prefer using DateAdd, it is perfectly valid to add days directly - though you might want to consider if you're actually wanting to add 30 days versus adding 1 month.
NOTE: On versions prior to CF10 you'll need to split the DateTimeFormat into DateFormat and TimeFormat and update the masks accordingly.