s.events is giving undefined

Or you can check if there is any value in s.events like so:

Basically this is a shorthand if statement:

If s.events has a value

THEN

use s.events + ",event140=xyz" (notice the comma)

ELSE
use "event140=xyz" (no comma)

If there is no s.events then you should just get: "event140=xyz" 

If s.events is say "event12", then you should get "event12,event140=xyz"

If s.events is "event13,", then you should get "event13,,event140=xyz"

Not sure how worried you are about having 2 commas (that would drive me crazy, lol).. but you could fix that by replacing ",," with "," if it bothers you.

Hey @sa30 

There is a common analytics plugin available for this which is appendToList. It is used to append a value to existing set of values as the name suggests.

I have put a few examples from the official documentation link (https://experienceleague.adobe.com/docs/analytics/implementation/vars/plugins/apl.html?lang=en) below and highlighted your use case.

// Set the events variable to "event22,event24,event23".

s.events = "event22,event24";
s.events = apl(s.events,"event23");

// The events variable remains unchanged because the apl function does not add duplicate values

s.events = "event22,event23";
s.events = apl(s.events,"event23");

// Set the events variable to "event23" if the events variable is blank

s.events = "";
s.events = apl(s.events,"event23");

// Append a value to eVar5. The value of prop4 remains unchanged.
// The value of eVar5 is "hello|people|today".

s.prop4 = "hello|people";
s.eVar5 = apl(s.prop4, "today", "|");

// Sets prop4 to "hello|people,today". Be mindful of correct delimiters!

s.prop4 = "hello|people";
s.prop4 = apl(s.prop4, "today");

// Sets the events variable to "event22,event23,EVentT23". Be mindful of capitalization when using the cc argument!

s.events = "event22,event23";
s.events = apl(s.events,"EVenT23", ",", ",", true);

// Sets the events variable to "event22,event23,event24,event25".

s.events = "event22,event23";
s.events = apl(s.events, "event23,event24,event25");

// Sets linkTrackVars to "events,eVar1,campaign".
// The last three arguments at the end of this apl call are not necessary because they match the default argument values.

s.linkTrackVars = "events,eVar1";
s.linkTrackVars = apl(s.linkTrackVars, "campaign", ",", ",", false);

// This apl call does not do anything because the code does not assign the returned value to a variable.

s.events = "event22,event24";
apl(s.events, "event23");

// Sets the list2 variable to "apple-APPLE-Apple".
// Since the two delimiter arguments are different, the value passed in is delimited by "|", then joined together by "-".

s.list2 = "apple|APPLE";
s.list2 = apl(s.list2, "Apple", "|", "-", true);

// Sets the list3 variable to "value1,value1,value1" (unchanged).
// Only new values are deduplicated. Existing duplicate values remain.

s.list3 = "value1,value1,value1";
s.list3 = apl(s.list3,"value1");

Hope the above helps. This plugin is used quite extensively.

Regards,

Abhinav