MEPX
Chapter 9 of 16All chapters
  1. 1Introduction
  2. 2Syntax and statements
  3. 3Variables and scope
  4. 4Data types
  5. 5Comparison and coercion
  6. 6Strings
  7. 7Numbers and maths
  8. 8Arrays
  9. 9Objects
  10. 10Functions
  11. 11Conditions and loops
  12. 12Classes
  13. 13The DOM
  14. 14Events
  15. 15Promises and async
  16. 16Modules

Chapter 9 of 16

Objects

Key and value pairs, and how they are copied.

Reading and writing

An object maps string keys to values, read with dot or bracket notation. Optional chaining, user?.address?.city, stops a missing middle from throwing.

  • Destructuring pulls fields out: const { name, age } = user.
  • Spread copies: const copy = { ...user, name: "Ada" }.

References

Objects are held by reference, so assigning one to a second variable does not copy it. Spread makes a shallow copy, and structuredClone makes a deep one when nested objects must be independent.