Arrays.

Data chapter. Foundations gave you numbers one by one. Now we hold a list of amounts — an array.

Square brackets: const amounts = [12, 25, 40]; Order matters. amounts.length returns the count (here 3).

Mini example:

const tips = [5, 5, 10]; console.log(tips.length);

Common mistake: amounts = 12 (one number); or amounts.size instead of .length (that belongs to other structures).