How to Use Conditional Statements in JavaScript

// if/else
const age = 18;

if (age >= 18) {
  console.log("Adult");
} else if (age >= 13) {
  console.log("Teenager");
} else {
  console.log("Child");
}

// Ternary operator
const status = age >= 18 ? "Adult" : "Minor";
console.log(status);

// Truthy and falsy values
const values = [0, "", null, undefined, NaN, false, "hello", 42, [], {}];

values.forEach(value => {
  if (value) {
    console.log(`Truthy: ${value}`);
  } else {
    console.log(`Falsy: ${value}`);
  }
});

// Nullish coalescing (??)
const username = null;
const displayName = username ?? "Anonymous";
console.log(displayName);

// Optional chaining (?.)
const user = { profile: { name: "Alice" } };
console.log(user.profile?.name); // Alice
console.log(user.address?.city); // undefined (no error)

// Switch statement
const day = "Monday";

switch (day) {
  case "Monday":
  case "Tuesday":
  case "Wednesday":
  case "Thursday":
  case "Friday":
    console.log("Weekday");
    break;
  case "Saturday":
  case "Sunday":
    console.log("Weekend");
    break;
  default:
    console.log("Invalid day");
}

// Logical operators
const a = true;
const b = false;

console.log(a && b); // false (AND)
console.log(a || b); // true (OR)
console.log(!a); // false (NOT)

// Short-circuit evaluation
const user2 = null;
const name = user2 && user2.name; // null
const defaultName = user2 || "Guest"; // "Guest"