Event Driven GUI, Looping Through An Array

I have an associative array that I need to loop through, allbills,
however, each element in this array requires processing by the user and
I need to capture the users actions on the element and then return to
the next element in the list but suspend looping until I have the users
desired action...

For example,

for(mybill in allbills)
{
GetWhatToDo(mybill); // gets the information about what user wants to
do with the currentBill
}

The problem is that the function "GetWhatToDo" doesn't "block" so the
loop completes without waiting for the users input from GetWhatToDo...

So, my thought was I need to design things more 'event-driven' and
handle things like so:

function handleABill() {
mybill=GetNextBill();
GetWhatToDo(mybill);
}

A "Next" button inside the popup generated by GetWhatToDo will have an
onclick event that calls handleABill again...

The problem is that I can't figure out how to write GetNextBill so that
it maintains the state of the loop through 'allbills', especially since
'allbills' is an associative array and I can't keep track of the array
index. The only thing I can think of is to initialize a regular array
from the associative array and keep track of the index number.