MEPX
Chapter 10 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 10 of 16

Functions

Declarations, arrow functions and this.

Three ways to write one

A function declaration is hoisted and can be called before its line. A function expression is not. An arrow function is shorter and returns an expression without the return keyword when written on one line.

  • Default parameters and rest parameters cover most argument juggling.
  • Functions are values, so they can be passed around and returned.

What this means

In a normal function, this depends on how the function was called. An arrow function has no this of its own and borrows the surrounding one, which is why arrows are the safe choice inside callbacks.