Discussion on: Typical JavaScript interview exercises (explained)

[Rich Seviora]

To be very thorough:

Object.freeze(heroes);
const newHeroes = heroes.map(h => {
  Object.freeze(h);
  return { ...h, name: h.name.toUpperCase() }
})

[JDucharme]

This approach is the only one that seems to work for me.

[David Miller]

Why would you need to freeze it? This stuff is synchronous, how would it change in the middle of your operation?

[Rich Seviora]

It's to guard against future changes. But the requirement was to "preserve immutability" and so this makes the original data set immutable going forward.