Why error handling is required in Javascript - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why do we need error handling in JavaScript?

Which of the following best explains why error handling is important in JavaScript programs?

A It prevents the program from ever stopping or crashing, no matter what.

B It makes the program run faster by skipping error checks.

C It helps the program continue running smoothly even when unexpected problems occur.

D It automatically fixes all bugs in the code without programmer input.

💡 Hint

Think about what happens if something goes wrong in a program without any way to handle it.

Error handling allows a program to manage unexpected problems gracefully, so it can keep working or provide useful messages instead of crashing.

❓ Predict Output

intermediate

Output with and without error handling

What will be the output of the following JavaScript code?

function divide(a, b) {
  return a / b;
}

console.log(divide(10, 0));

Javascript

function divide(a, b) {
  return a / b;
}

console.log(divide(10, 0));

A Error: Division by zero

B 0

C NaN

D Infinity

💡 Hint

In JavaScript, dividing a number by zero does not throw an error but returns a special value.

JavaScript returns Infinity when dividing a positive number by zero instead of throwing an error.

❓ Predict Output

advanced

What error is thrown without try-catch?

What error will this code produce when run?

const obj = null;
console.log(obj.name);

Javascript

const obj = null;
console.log(obj.name);

A TypeError: Cannot read property 'name' of null

B ReferenceError: obj is not defined

C SyntaxError: Unexpected token '.'

D undefined

💡 Hint

Accessing a property on null causes a specific type of error in JavaScript.

Trying to access a property on null throws a TypeError because null is not an object.

🧠 Conceptual

advanced

Benefits of using try-catch blocks

Which of the following is NOT a benefit of using try-catch blocks in JavaScript?

A They automatically fix the errors in the code.

B They allow the program to handle errors without stopping execution abruptly.

C They can provide custom error messages to users.

D They help in debugging by catching and logging errors.

💡 Hint

Think about what try-catch blocks do and what they do not do.

Try-catch blocks help manage errors but do not fix the errors automatically; fixing requires programmer action.

🚀 Application

expert

Predict output with nested try-catch and finally

What will be the output of this JavaScript code?

function test() {
  try {
    console.log('Start');
    throw new Error('Oops');
  } catch (e) {
    console.log('Caught:', e.message);
    return 'From catch';
  } finally {
    console.log('Finally block');
    return 'From finally';
  }
}

console.log(test());

Javascript

function test() {
  try {
    console.log('Start');
    throw new Error('Oops');
  } catch (e) {
    console.log('Caught:', e.message);
    return 'From catch';
  } finally {
    console.log('Finally block');
    return 'From finally';
  }
}

console.log(test());

A

Start
Caught: Oops
Finally block
From catch

B

Start
Caught: Oops
Finally block
From finally

C

Start
Finally block
Caught: Oops
From finally

D

Start
Caught: Oops
From catch
Finally block

💡 Hint

Remember that a return in finally overrides previous returns.

The finally block runs after catch and its return overrides the catch return, so the function returns 'From finally'.