Copy vs Mutate.

Eighth class. In Data you saw alias versus copy. Here we apply that to sorting and edits.

If you make copy = [...amounts] or amounts.slice(), sorting copy does not touch the original. If you sort the original array, it changes.

Mini example:

const amounts = [40, 12]; const copy = [...amounts]; copy.sort((a, b) => a - b); console.log(amounts); console.log(copy);

Common mistake: sorting the original list when you meant to keep order; or thinking alias = amounts is a copy.