JavaScript Functions

What you'll learn

• Why functions being values is the single fact that unlocks the rest
• How closures actually work — the lexical scope mechanism, not the metaphor
• The four rules that decide what `this` points to, in priority order
• Higher-order functions, and why map/filter/reduce feel natural once you see them
• Currying and partial application — what each is for, and when to reach for which
• The bugs that bite every JavaScript developer at least once, and how to spot them

1. 01
   Functions are values

   The one fact about JS functions that unlocks every fancy pattern that comes later.
   12 min
2. 02
   Declarations vs expressions

   Three ways to make a function. Why hoisting only applies to one of them.
   13 min
3. 03
   Parameters and arguments

   Defaults, rest, destructuring, and the legacy arguments object you can mostly ignore.
   14 min
4. 04
   Closures

   Why a returned function still remembers the variables around it. The mechanism, not just the metaphor.
   18 min
5. 05
   this, finally

   The four binding rules in priority order. Stop guessing what this points to.
   16 min
6. 06
   Arrow functions

   No own this, no arguments, no new. Why that fixes callbacks and breaks methods.
   12 min
7. 07
   Higher-order functions

   Functions that take functions, return functions, or both. Where map/filter/reduce come from.
   13 min
8. 08
   Currying and partial application

   Two related ideas, side by side. When each is the right tool, and what bind has to do with it.
   11 min
9. 09
   Common pitfalls

   The classic JS function bugs — the var loop trap, lost this, accidental globals, shared state.
   11 min