🧠 MODULE 1: JavaScript Core (Very Deep Dive)

If you're serious about becoming a strong JavaScript developer (especially as a full-stack dev), this module is your foundation. These are not just interview topics — they shape how JavaScript thinks . Let’s break them down clearly, deeply, and in a practical human way. ✅ 1.1 Language Fundamentals 🔹 1. var , let , const These are used to declare variables — but they behave very differently. var Function scoped Can be redeclared Hoisted (initialized as undefined ) Causes bugs in modern code var x = 10 ; var x = 20 ; // Allowed ⚠️ Avoid in modern JS unless you understand legacy behavior. let Block scoped Cannot be redeclared in same scope Hoisted but in Temporal Dead Zone let count = 5 ; count = 6 ; // Allowed const Block scoped Cannot be reassigned Must be initialized const PI = 3.14 ; ⚠️ Important: const does NOT make objects immutable — it only prevents reassignment. const user = { name : " Nadim " }; user . name = " John " ; // Allowed 🔹 2. Scope (Block vs Function) Scope determines