Operators & Expressions

// Basic arithmetic
let sum = 5 + 3;          // => 8    (addition)
let diff = 10 - 4;        // => 6    (subtraction)
let product = 4 * 3;      // => 12   (multiplication)
let quotient = 15 / 4;    // => 3.75 (division)
let remainder = 15 % 4;   // => 3    (modulo/remainder)
let power = 2 ** 4;       // => 16   (exponentiation)

// String concatenation with +
let greeting = "Hello " + "World";  // => "Hello World"

// Careful: + with mixed types
console.log(1 + "2");      // => "12" (number coerced to string)
console.log("3" + 4 + 5); // => "345" (left to right: "3"+4 = "34", "34"+5 = "345")
console.log(3 + 4 + "5"); // => "75"  (3+4 = 7, then 7+"5" = "75")

let count = 5;

// Post-increment: returns value THEN increments
console.log(count++);     // => 5
console.log(count);       // => 6

// Pre-increment: increments THEN returns value
console.log(++count);     // => 7
console.log(count);       // => 7

// Decrement works the same way
let x = 10;
console.log(x--);         // => 10
console.log(x);           // => 9
console.log(--x);         // => 8

// Strict equality (recommended)
console.log(5 === 5);      // => true
console.log(5 === "5");    // => false (different types)

// Strict inequality
console.log(5 !== "5");    // => true
console.log(5 !== 5);      // => false

// Loose equality (avoid)
console.log(5 == "5");     // => true  (coerces types)
console.log(0 == false);   // => true  (coerces!)
console.log("" == false);  // => true  (coerces!)

// Relational
console.log(10 > 5);       // => true
console.log(10 < 5);       // => false
console.log(10 >= 10);     // => true
console.log(10 <= 5);      // => false

// String comparison (lexicographic, by Unicode order)
console.log("apple" < "banana");  // => true ('a' comes before 'b')
console.log("Apple" < "apple");   // => true (uppercase < lowercase)

let a = true;
let b = false;

// AND (&&) — true only if both operands are true
console.log(a && b);        // => false
console.log(true && true);  // => true

// OR (||) — true if at least one operand is true
console.log(a || b);        // => true
console.log(false || false); // => false

// NOT (!) — inverts boolean
console.log(!a);            // => false
console.log(!b);            // => true
console.log(!!"hello");     // => true (double NOT converts to boolean)

// && — if left is falsy, return left; otherwise return right
console.log(false && "anything");  // => false  (short-circuits)
console.log(true && "result");     // => "result"

// || — if left is truthy, return left; otherwise return right
console.log("hello" || "fallback"); // => "hello" (short-circuits)
console.log("" || "fallback");      // => "fallback"

// Practical: default values
const username = userInput || "Guest";

// Practical: conditional execution
isLoggedIn && renderDashboard();  // Only calls renderDashboard if isLoggedIn is true

// ?? returns right side only if left is null or undefined
let value1 = null;
let value2 = undefined;
let value3 = false;

console.log(value1 ?? "default");   // => "default"
console.log(value2 ?? "default");   // => "default"
console.log(value3 ?? "default");   // => false (not null/undefined)

let x = 10;

x += 5;     // x = x + 5   => 15
x -= 3;     // x = x - 3   => 12
x *= 2;     // x = x * 2   => 24
x /= 4;     // x = x / 4   => 6
x %= 2;     // x = x % 2   => 0
x **= 3;    // x = x ** 3  => 0 (0^3)

// More concise increments
let count = 0;
count += 1;  // => 1

// Syntax: condition ? valueIfTrue : valueIfFalse
const age = 20;
const status = age >= 18 ? "Adult" : "Minor";
console.log(status);  // => "Adult"

// Nested ternary (use sparingly — can be hard to read)
const score = 85;
const grade = score >= 90 ? "A" : score >= 80 ? "B" : score >= 70 ? "C" : "F";
console.log(grade);   // => "B"

// PEMDAS-like: * and / before + and -
let result = 2 + 3 * 4;          // => 14 (3*4=12, 12+2=14)
let result2 = (2 + 3) * 4;       // => 20 (2+3=5, 5*4=20)

// Comparison operators have lower precedence than arithmetic
let check = 5 + 3 > 2 + 4;       // => true (8 > 6)
let check2 = 5 + (3 > 2) + 4;    // => 10   (5 + true(1) + 4)

// Logical operators: NOT > AND > OR
console.log(true || false && false);        // => true  (&& first: false && false = false, then true || false = true)
console.log((true || false) && false);      // => false (|| first: true || false = true, then true && false = false)

// 1. What is the result of 10 + "5"? Why?
// 2. What is the result of 10 - "5"? Why?
// 3. Is 0 == false? Is 0 === false?
// 4. What does "5" + 3 + 2 evaluate to?
// 5. What does 5 + 3 + "2" evaluate to?
// 6. Use the ternary operator to check if a number is even or odd
// 7. Use || to provide a default value for a variable

const num = 7;
const parity = num % 2 === 0 ? "even" : "odd";
console.log(`${num} is ${parity}`);  // => "7 is odd"