It would be very useful if substring could accept a length parameter greater then the length of the string without erroring.
Ideally it would be great to have left() and right() functions, as well as substring() for simply obtaining the first and last 'n' characters of a string.
In the substring, we are unable to execute on if condition based. if my answer value is 'na'. Then it should not execute the true condition.
if(greaterOrEquals(length(triggerBody()['answer6']), 4), substring(triggerBody()['answer6'],sub(length(triggerBody()['answer6']), 4),4), '')
@take() provides you with the first n characters and @skip() can get you the last n characters (using length()-n).