Displaying a Partial List Array?

Question

Hi, I'm trying to figure out how to take an existing array of
elements (for sake of argument, earth, air, fire, water), and have
a text display list as the base, +/- based on button behavior.
So, for example, if I begin with earth, air
and click the add button, it will switch to "earth, air,
fire"
if I click the add button again, it will display the four
elements "earth, air,fire, water", and if I click the subtract
button, it will subtract from the list (earth, air, fire... earth,
air.... earth... undefined).
The idea is to be able to go from a completely empty list
(undefined) to completely full (such as four elements) and back, in
increments of one. String(aElements.pop()); works fine for removing
elements from the list, but
aElements.push("___"); is completely insufficient for the
task.
Ideas?

Answer 1

integer should be restricted so it's never less than zero.
but there's no reason to use a variable to track the next index of
the element to add to aNewElements:
to remove: aNewElements.pop();
to add:
aNewElements.push(aElements[aNewElements.length]);