⚠️ Day 38 — Async Error Handling & Try/Catch

Hi Guys Welcome to Day 38 🚨 JavaScript is powerful, but errors are inevitable — a server might fail, a network could drop, or invalid data might appear. That’s why learning **error handling** is critical for every real-world developer. Today, we’ll explore try/catch, async error management, and custom error handling.

🧠 1️⃣ What is Error Handling?

Error handling ensures your app continues to work gracefully even when something goes wrong. Without it, one failure could crash your entire script.

try {
  let data = JSON.parse('{ name: "Rahul" }'); // ❌ invalid JSON
} catch (err) {
  console.log("Something went wrong:", err.message);
}

The try block tests the code; catch handles the error without breaking the app.

🧩 2️⃣ Finally Block

You can use finally to execute code whether an error happens or not — ideal for cleanup operations.

try {
  console.log("Starting process...");
  throw new Error("Unexpected error occurred!");
} catch (error) {
  console.log("Caught:", error.message);
} finally {
  console.log("Process ended.");
}

⚙️ 3️⃣ Async Error Handling with Fetch

When using Fetch API, network issues can occur — use try/catch with async/await.

async function getData(){
  try {
    const res = await fetch("https://jsonplaceholder.typicode.com/invalidURL");
    if(!res.ok) throw new Error("Server returned " + res.status);
    const data = await res.json();
    console.log(data);
  } catch (err) {
    console.error("Error fetching data:", err.message);
  } finally {
    console.log("Fetch attempt completed.");
  }
}
getData();

💡 4️⃣ Custom Error Throwing

You can create your own errors for specific conditions — helpful for validation.

function validateUser(user) {
  if (!user.name) throw new Error("Name is required!");
  if (user.age < 18) throw new Error("User must be 18+!");
  console.log("User validated successfully.");
}

try {
  validateUser({ name: "", age: 16 });
} catch (err) {
  console.log("Validation failed:", err.message);
}

🧮 5️⃣ Promise Error Handling

If you’re using Promises instead of async/await, you can handle errors using .catch().

fetch("https://jsonplaceholder.typicode.com/posts/1000")
  .then(res => {
    if(!res.ok) throw new Error("Resource not found!");
    return res.json();
  })
  .then(data => console.log(data))
  .catch(err => console.error("Promise Error:", err.message));

🧠 6️⃣ Real-Life Example: Login Validation

Imagine a login API call — here’s how you’d handle success and failure gracefully.

async function loginUser(email, password) {
  try {
    if(!email || !password) throw new Error("Please enter all fields!");

    const res = await fetch("https://reqres.in/api/login", {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify({ email, password })
    });

    if(!res.ok) throw new Error("Invalid credentials");

    const data = await res.json();
    console.log("Login successful:", data);
  } catch (error) {
    console.error("Login failed:", error.message);
  }
}
loginUser("test@example.com", "wrongpass");

🎯 Summary

Error handling isn’t about avoiding mistakes — it’s about managing them. Today you learned try/catch/finally, async/await error flow, and how to throw custom exceptions like a professional developer. Tomorrow, you’ll store data permanently using Web Storage APIs — LocalStorage, SessionStorage, and Cookies.

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