Managing JavaScript Errors with try, catch, and finally

try {
  // 🎯 RISKY code — might throw an error
} catch (error) {
  // 🥅 runs ONLY if an error was thrown — "error" holds the details
} finally {
  // 🧹 runs ALWAYS — error or not
}

try {
  const user = JSON.parse("this is not valid JSON");
  // 💥 throws!
  console.log("This never runs ⏭️");
  // skipped entirely
} catch (error) {
  console.log("❌ Invalid data — but the app survives!");
  console.log(`Details: ${error.message}`);
}console.log("Welcome! 👋");
// ✅ runs — the app LIVED!

❌ Invalid data — but the app survives!Details: Unexpected token 'h', "this is no"... is not valid JSONWelcome! 👋

try {
  undefinedVariable;
  // 💥 ReferenceError
} catch (error) {
  console.log(error.name);
  // "ReferenceError" — the type
  console.log(error.message);
  // "undefinedVariable is not defined" — details
  console.log(error.stack);
  // the full stack trace (file + lines)
}

try {
  JSON.parse(input);
} catch {
  // no (error) needed ✅
  showDefaultData();
}

function loadDashboard() {
  console.log("⏳ Loading spinner ON");
  try {
    const data = fetchDashboardData();
    // might fail!
    console.log("✅ Data loaded:", data);
  } catch (error) {
    console.log("❌ Load failed — showing cached data");
  } finally {
    console.log("⏳ Loading spinner OFF");
    // 🧹 ALWAYS runs!
  }
}

function setAge(age) {
  if (typeof age !== "number" || isNaN(age)) {
    throw new TypeError("Age must be a number! 🔢");
    // specific type
  } if (age < 0 || age > 120) {
    throw new RangeError("Age must be between 0 and 120! 🚫");
  } console.log(`✅ Age set to ${age}`);
  return age;
}try {
  setAge(25);
  // ✅ Age set to 25
  setAge(-5);
  // 💥 throws RangeError
} catch (error) {
  console.log(`${error.name}: ${error.message}`);
  // "RangeError: Age must be between 0 and 120! 🚫"
}

throw new Error("message");
// generic error
throw new TypeError("message");
// wrong type (Lesson 44's family!)
throw new RangeError("message");
// out of range

try {
  processUserInput(maybeBadInput);
} catch (error) {
  if (error instanceof TypeError) {
    console.log("🔢 Data problem:", error.message);
  } else if (error instanceof RangeError) {
    console.log("📏 Range problem:", error.message);
  } else {
    console.log("💥 Unexpected:", error);
    throw error;
    // 🔄 re-throw what you can't handle!
  }
}

async function loadUser(id) {
  showSpinner();
  try {
    const response = await fetch(`https://jsonplaceholder.typicode.com/users/${id}`);
    if (!response.ok) {
      throw new Error(`HTTP ${response.status} — user not found 🔍`);
    } const user = await response.json();
    console.log(`👤 Loaded: ${user.name}`);
  } catch (error) {
    console.log(`❌ Couldn't load user: ${error.message}`);
    showErrorMessage("Something went wrong — please retry 🔄");
  } finally {
    hideSpinner();
    // 🧹 spinner off, success or fail ✅
  }
}

try {
  setTimeout(() => {
    throw new Error("💥");
    // 😱 escapes the try/catch!
  }, 1000);
} catch (error) {
  console.log("never catches this");
  // the timer fires AFTER try/catch finished
}