Error Handling in JavaScript

📘 What is Error Handling?

Error handling is the process of responding to and managing exceptions (errors) that occur during the execution of code, allowing programs to recover gracefully instead of crashing.

⚠️ Why Do Errors Occur?

Incorrect syntax
Calling undefined variables/functions
Runtime failures (e.g., failed API calls)
Invalid user input

✅ How to Handle Errors in JS?

try {
  let data = JSON.parse("{ invalid json }");
} catch (error) {
  console.error("Caught an error:", error.message);
} finally {
  console.log("This always runs.");
}

🔁 Try, Catch, Finally Explained

try: Code to test for errors
catch: Handles the error
finally: Always runs

🧨 Throwing Errors Manually

function divide(a, b) {
  if (b === 0) throw new Error("Cannot divide by zero!");
  return a / b;
}

🧱 JavaScript Error Object

name – Type of error
message – Details about the error
stack – Call stack trace

⚙️ Common Error Types

ReferenceError
TypeError
SyntaxError
RangeError
EvalError
URIError

⏳ Async & Await async/await

Know more in Detail

async function fetchUser() {
  try {
    let res = await fetch("https://jsonplaceholder.typicode.com/users/1");
    let user = await res.json();
    console.log(user);
  } catch (err) {
    console.error("Failed to load user:", err.message);
  }
}

🧪 Live Demo: Error Catching in Action

📚 Practice Questions

Create a program to convert string to JSON. Catch and log errors if the string is malformed.
Write a function that fetches data from an API using async/await and handles failures.
Simulate a login function that throws an error if username or password is empty.
Try dividing two user inputs and handle division by zero.
Create a custom error message using throw if age input is less than 18.

❓ FAQ

What happens if an error is not caught?

The script will stop running and a message will be shown in the browser console.

Can you use try-catch with async functions?

Yes, wrap the await calls in a try-catch block to handle asynchronous errors.

Should I always use try-catch?

Use it when you expect possible runtime errors and want to prevent app crashes.

What is the difference between try-catch and .catch() on promises?

try-catch works with async/await, while .catch() is used with promise chains.

🧠 Final Summary

Errors are common in JS, handling them improves UX and stability
Use try-catch and throw to trap and define issues
Async functions must also handle errors using try-catch
Practice handling all types: sync, async, custom