JavaScript If Else

function getGrade(marks) {
  if (marks < 0 || marks > 100) {
    return "Invalid marks (must be 0-100)";
  }
  
  if (marks >= 90) return "A+ — Excellent!";
  if (marks >= 80) return "A — Very Good";
  if (marks >= 70) return "B — Good";
  if (marks >= 60) return "C — Average";
  if (marks >= 50) return "D — Below Average";
  return "F — Fail";
}

const students = [
  { name: "Asha", marks: 95 },
  { name: "Ravi", marks: 78 },
  { name: "Priya", marks: 55 },
  { name: "Mira", marks: 42 },
  { name: "Karan", marks: 88 }
];

students.forEach(student => {
  console.log(student.name + ": " + getGrade(student.marks));
});

// ─── Simple ternary ──────────────────────────────────────────────
const isLoggedIn = true;
const buttonText = isLoggedIn ? "Logout" : "Login";
console.log(buttonText); // Logout

// ─── Ternary in JSX-style string template ──────────────────────────
const cartCount = 3;
const cartDisplay = cartCount > 0
  ? "Cart (" + cartCount + " items)"
  : "Cart (empty)";
console.log(cartDisplay); // Cart (3 items)

// ─── Ternary for class names (common in React) ─────────────────────
const isDarkMode = false;
const theme = isDarkMode ? "dark-theme" : "light-theme";
console.log("Theme:", theme);

// ─── Nested ternary (use sparingly) ───────────────────────────────
const score = 75;
const grade = score >= 90 ? "A"
  : score >= 70 ? "B"
  : score >= 50 ? "C"
  : "F";
console.log("Grade:", grade);

// ── && (AND): execute right side ONLY if left is truthy ────────────
const user = { name: "Asha", isAdmin: true, isVerified: true };

// Classic pattern: condition && action
user.isAdmin && console.log("Admin panel available");
user.isVerified && user.isAdmin && console.log("Super admin confirmed");

// ── || (OR): use fallback if left is falsy ────────────────────────
const username = "";          // empty string = falsy
const displayName = username || "Anonymous User";
console.log(displayName);     // Anonymous User

const config = null;
const timeout = config?.timeout || 3000;  // default 3 seconds
console.log("Timeout:", timeout);

// ── ?? (Nullish Coalescing): fallback for null/undefined ONLY ─────
const count = 0;
console.log(count || "No count");    // "No count" ← 0 is falsy!
console.log(count ?? "No count");   // 0 ← 0 is not null/undefined ✅

// ── Real pattern: guard clause ──────────────────────────────────────
function updateProfile(userId, data) {
  if (!userId) return { error: "User ID required" };
  if (!data || Object.keys(data).length === 0) return { error: "No data provided" };
  
  return { success: true, message: "Profile updated" };
}

console.log(updateProfile(null, { name: "Asha" }));
console.log(updateProfile(42, {}));
console.log(updateProfile(42, { name: "Asha" }));