Functions and loop boundaries

The idea

A function names a transformation from arguments to a result. Its parameters are local bindings, and return sends a value to the caller while ending that invocation. Printing is a separate side effect: console.log helps inspection but does not replace a return value. State accepted inputs and the required output before writing the body.

Loops repeat a controlled step. For an array, indices begin at zero and the last valid index is length minus one, so a less-than comparison is usually the correct upper bound. An accumulator records progress between iterations. Decide its starting value using the empty-input case, then verify that every iteration preserves the meaning you assigned to it.

function totalPositive(values) {
  let total = 0;
  for (const value of values) {
    if (value > 0) total += value;
  }
  return total;
}
console.log(totalPositive([3, -2, 4]));

7

The accumulator begins at zero and includes only positive values. The function also returns zero for an empty array.