TOPIC OVERVIEW

javascript/Functions

First-class values that carry their own scope, their own this, and sometimes their own surprises.

10 QuestionsIntermediateHigh Priority ~12 min read

Functions in JavaScript are first-class values — they can be assigned to variables, passed as arguments, returned from other functions, and stored in data structures, which is what makes patterns like callbacks, higher-order functions, and functional composition possible. But not all functions behave the same way: function declarations are hoisted in full, function expressions are not, and arrow functions differ from both in a way that goes deeper than syntax.

Arrow functions don't have their own this, arguments object, or prototype — they lexically inherit this from wherever they're defined, which makes them predictable inside callbacks but wrong for methods that need their own this. Regular functions, meanwhile, get a fresh this determined by how they're called, not where they're defined, which is the root of most 'why is this undefined' bugs.

What you'll walk away knowing

The difference between function declarations, function expressions, and arrow functions in hoisting and behavior

Why arrow functions don't bind their own this, and when that's the right or wrong choice

What a higher-order function is, and how functions being first-class values enables it

How default parameters, rest parameters, and the arguments object interact (and where arguments doesn't exist)

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