Error Handling in JavaScript: Try, Catch, Finally

⚠️ What Are Errors in JavaScript?

Errors are problems that occur during code execution and stop your program from running correctly.

🔹 Common Types of Errors

1. Syntax Error
   Mistake in code structure

   console.log("Hello" // missing )
   

2. Reference Error

   Using a variable that is not defined

   console.log(name); // name is not defined
   

3. Type Error

   Wrong operation on a data type

   let num = 10;
   num.toUpperCase(); // number has no toUpperCase()
   

4. Range Error

   Value out of allowed range

   let arr = new Array(-1);
   

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🚨 Real Runtime Error Example

let user = null;
console.log(user.name); // ❌ TypeError

👉 This crashes your app if not handled.

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🛠️ Using try...catch

try...catch helps handle errors gracefully instead of crashing.

try {
  let user = null;
  console.log(user.name);
} catch (error) {
  console.log("Something went wrong:", error.message);
}

✅ Output:

Something went wrong: Cannot read properties of null

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🔄 Execution Flow (Try → Catch → Finally)

Start
  ↓
Try Block
  ↓
Error?
 /   \
Yes   No
 ↓     ↓
Catch  Skip Catch
  ↓
Finally (always runs)
  ↓
End

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🧩 The finally Block

finally always runs — whether an error occurs or not.

try {
  console.log("Try block running");
} catch (err) {
  console.log("Error caught");
} finally {
  console.log("Always runs");
}

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🎯 Throwing Custom Errors

You can create your own errors using throw.

function withdraw(amount) {
  if (amount > 1000) {
    throw new Error("Limit exceeded");
  }
  return "Withdrawal successful";
}

try {
  withdraw(2000);
} catch (err) {
  console.log(err.message);
}

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🌍 Real-World Example (Bank System)

function transfer(balance, amount) {
  try {
    if (amount > balance) {
      throw new Error("Insufficient balance");
    }
    console.log("Transfer successful");
  } catch (err) {
    console.log("Transaction failed:", err.message);
  } finally {
    console.log("Transaction attempt completed");
  }
}

transfer(500, 700);

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💡 Why Error Handling Matters

✅ Prevents App Crash

Without handling → app stops ❌

With handling → app continues ✅

✅ Graceful Failure

Instead of breaking:

"Error occurred"

You show:

"Something went wrong, please try again"

✅ Better Debugging

• Error messages help identify bugs faster

• Stack traces show where the issue occurred

✅ Improves User Experience

Users don’t see broken screens 👍

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🧭 Graceful Failure Example

❌ Bad:

console.log(user.name);

✅ Good:

if (user) {
  console.log(user.name);
} else {
  console.log("User not available");
}

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🔍 Debugging Benefits

• Helps locate exact issue

• Saves development time

• Makes code maintainable

• Easier testing & logging

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🎯 Quick Summary

• Errors are unavoidable — handling them is essential

• Use try...catch to prevent crashes

• Use finally for cleanup tasks

• Use throw to create custom errors

• Always aim for graceful failure