Variables & Scoping

1// const — cannot be reassigned
2const name = "Skill-Forge";
3// name = "Other"; // TypeError!
4 
5// let — can be reassigned
6let score = 0;
7score = 100;
8console.log(score); // 100
9 
10// var — avoid in modern JS
11var old = "legacy";
12console.log(old);

1// Block scope with let
2if (true) {
3  let x = 10;
4  console.log(x); // 10
5}
6// console.log(x); // ReferenceError!
7 
8// Function scope with var
9function example() {
10  if (true) {
11    var y = 20;
12  }
13  console.log(y); // 20 — var leaks out of the if block!
14}
15example();

1const str = "hello";       // string
2const num = 42;            // number
3const bool = true;         // boolean
4const empty = null;        // object (known quirk)
5const notDefined = undefined; // undefined
6 
7console.log(typeof str);   // "string"
8console.log(typeof num);   // "number"
9console.log(typeof bool);  // "boolean"
10console.log(typeof empty); // "object"