MEPX
Chapter 11 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 11 of 16

Conditions and loops

Branching, iterating and stopping early.

Branching

if, else if and else cover most decisions, and switch suits a value with several known cases. The ternary a ? b : c is an expression, so it fits where a statement cannot go.

  • The ?? operator returns the right side only for null and undefined, unlike || which also fires on 0 and "".
  • Assign with ??= to fill in a missing value.

Loops

for...of walks values in an array or any iterable, for...in walks keys of an object, and while repeats until a condition fails. break leaves a loop and continue skips to the next round.