Functions

Defining a Function

Three ways to create functions. Function declarations are hoisted — usable before they appear in code. Function expressions are assigned to bindings and are not hoisted. Arrow functions (=>) provide a shorter syntax and don't bind their own this.

Parameters that aren't passed default to undefined. Extra arguments are silently ignored.

Closure

A function can reference variables from its enclosing scope, even after that scope has finished executing. This is closure — the function "closes over" its environment.

Closures enable powerful patterns: factory functions, data privacy, and callbacks that remember their context. Understanding closure is essential for understanding JavaScript.

Recursion

A function that calls itself. Every recursive function needs a base case to stop. Each call adds a frame to the call stack — too many calls without returning causes a stack overflow.

Recursion is elegant for tree-like problems but often slower than loops. Some problems (like traversing nested structures) are naturally recursive.

Growing Functions

Two natural ways to introduce a function: you spot repeated code, or you need a specific capability. Functions should do one thing. If you find yourself adding "and" to describe what a function does, it probably should be two functions.

Good naming matters more than good comments. A function called printZeroPaddedWithLabel is telling you it does too much.