JS Date Set
Date setters mutate the existing object. Clone the date first when another part of the program needs the original.
Where to run this
This example uses the JavaScript console playground. Select Run to execute it; the example does not run on this lesson page.
A practical example
const opening = new Date("2026-11-07T10:00:00Z");
const later = new Date(opening);
later.setUTCDate(later.getUTCDate() + 7);
console.log(later.toISOString());
What happens
The copy moves to 14 November while the original stays unchanged.