AI solution for JavaScript Coding Question on BFE.dev
23. create a sum()

One possible solution using closures is:

function sum(num1) {
  return function(num2) {
    if (num2) {
      return sum(num1 + num2);
    } else {
      return num1;
    }
  };
}

This function returns a new function each time it's called, that either adds a new number to the sum or returns the current sum if no argument is provided. The function keeps track of the current sum using closures.