Test your knowledge: JavaScript Objects

Review

1. How does the lesson update an object without mutating the original?

   Spreading an object into a new one copies its properties, and properties written after the spread win, so the new object carries the change while the original stands still. That is how larger programs stay predictable when several parts hold the same record.
2. Reading user.profile.email when profile may be missing — what does the lesson reach for?

   Optional chaining stops the walk when the left side is null or undefined, handing back undefined instead of throwing. Paired with ?? it describes a default in the same breath, which is how missing data stays a one-line story.
3. What does const { theme = "light" } = settings do when settings has no theme property?

   A default in the destructuring pattern covers a missing property, so theme comes out "light" instead of undefined. It is the same defaulting idea as function parameters, wearing pattern syntax.
4. A method found its total through this.orders. What is this there?

   this is the object the method was called on, so the same method walking this.orders reads whichever order book it was summoned against. That is what lets one method serve every record shaped like it.
5. Why does property access sometimes use brackets instead of a dot?

   Bracket access takes any string expression, so a key that arrives in a variable, or one with spaces or dashes in it, can still be reached. Dots read names literally, which is exactly their convenience and exactly their limit.