JavaScript Functions Explained: return, console.log, Closures and Async Basics

A beginner-focused guide breaks down how JavaScript functions work, distinguishing between console.log as a side effect and return as a value-passing mechanism. The article explains that a function call always resolves to a value — either the returned result or undefined by default if no return statement executes. Using consistent examples with variables a=5 and b=10, it walks through four core variations of functions with and without console.log or return statements. It also covers parameters versus arguments, default parameter values, and why inner print statements appear before outer ones during nested calls. The guide aims to demystify common JavaScript output surprises by anchoring them to two foundational concepts: side effects and return values.