Iterating through Arrays with for Loops In the last challenge, we used a for loop to build up an array. Often, you'll want iterate through an already-existing array. (Iterate here just means to work with each value, one at a time, in order.) Let's rewrite our add function to see how to use a for loop to do so. The trick is defining the loop's condition. We want to start at the zeroth index, then the first index, then the second, and so on until we reach the last index. To do so, here's what the condition should do: Initialize a loop variable: let index = 0. Define an ending condition: index < list.length. Update the loop variable: index = index + 1. Now that we know how to write the condition, let's write the whole function: Create a variable, sum, and set it to 0. Create a for loop. See above for how to structure its condition. Inside the loop body, add list[index] to sum and store the result as sum. Outside the loop, return sum.