Error: undefined is not a function

I wrote the above code which is supposed to run through a list of names (referred to in the code using the variable allClientNames). It is supposed to run the function createBillMonthly() for each name in the list. (only if checkUnbilledAmount is greater than zero).
I am getting the error "undefined is not a function" when I try running it.
How can I fix that?

Hello, two things:

var i = 0; => {
    // the rest of your code goes here
while (helper.value == false) {
    // your code here