• Data Types: undefined, null, boolean, number, string, object, symbol, bigint
• Variables & Scope: var, let, const, block scope, global scope
• Operators: arithmetic operators, comparison operators, logical operators, bitwise operators
• Control Flow: if/else, switch, for/while loops, break/continue
• Functions: function declarations, function expressions, arrow functions (brief mention, detailed in ES6+)
• Type Coercion: implicit vs. explicit conversion
• Equality: == vs. ===
• Strict Mode: "use strict" - meaning and effects
• Closure
• this

Variable Declarations

let a = 10; // Block-scoped variable
const PI = 3.14; // Constant (cannot be reassigned)
var b = 20; // Function-scoped variable (not recommended)

Data Types

let num = 10;           // Number
let str = "Hello";      // String
let flag = true;        // Boolean
let arr = [1, 2, 3];    // Array (object)
let obj = { name: "JS" }; // Object
let undef;              // Undefined
let empty = null;       // Null

Type Checking

console.log(typeof 42); // "number"
console.log(typeof "Hi"); // "string"
console.log(typeof null); // "object" (JavaScript bug!)
console.log(typeof undefined); // "undefined"

Operators

Arithmetic Operators

let a = 5, b = 2;
console.log(a + b); // 7
console.log(a - b); // 3
console.log(a * b); // 10
console.log(a / b); // 2.5
console.log(a % b); // 1
console.log(a ** b); // 25 (Exponentiation)

Comparison Operators