Adam Enbar, Flatiron School's cofounder, believes now is the time to grow. Up to this point, we've been using console. Just pass an object as first parameter in the function call and object property which you want as second parameter. If there is no starting value provided, then for the first execution of the callback when there is no previous value the first parameter to the callback will be the value of the first element of the array, and the reduction starts with the second element. For this example, we start the sum at 0.