Error events and handling in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to listen for an error event on a Node.js EventEmitter.

Node.js

const EventEmitter = require('events');
const emitter = new EventEmitter();
emitter.on('error', [1] => {
  console.error('Error occurred:', [1].message);
});

Drag options to blanks, or click blank then click option'

Aevent

Berror

Cerr

De

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'event' or 'error' as the parameter name without matching usage inside the function.

Not providing a parameter to the callback function.

The error event handler receives the error object as the first argument. Using err is a common convention.

2fill in blank

medium

Complete the code to emit an error event with a custom error message.

Node.js

const EventEmitter = require('events');
const emitter = new EventEmitter();
emitter.emit('error', new [1]('Something went wrong'));

Drag options to blanks, or click blank then click option'

AException

BMessage

CEvent

DError

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent class like 'Exception' or 'Message'.

Passing a string directly instead of an Error object.

In Node.js, errors are usually instances of the built-in Error class.

3fill in blank

hard

Fix the error in the code to properly handle errors emitted by the EventEmitter.

Node.js

const EventEmitter = require('events');
const emitter = new EventEmitter();

emitter.on('error', function([1]) {
  console.log('An error happened:', [1].message);
});

Drag options to blanks, or click blank then click option'

Aerr

Berror

Cthis

Devent

Attempts:

3 left

💡 Hint

Common Mistakes

Not defining a parameter in the callback function.

Using 'this' to access the error object.

The error handler function must accept the error object as a parameter to access its properties.

4fill in blank

hard

Fill both blanks to create an error handler that logs the error stack and exits the process.

Node.js

emitter.on('error', ([1]) => {
  console.error([2].stack);
  process.exit(1);
});

Drag options to blanks, or click blank then click option'

Aerr

Berror

Ce

Devent

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the parameter and inside the function.

Trying to access stack on a variable that is not the error object.

The error object is passed as a parameter, commonly named err, and its stack property shows the error trace.

5fill in blank

hard

Fill all three blanks to create a try-catch block that emits an error event on failure.

Node.js

try {
  JSON.parse([1]);
} catch ([2]) {
  emitter.emit([3], [2]);
}

Drag options to blanks, or click blank then click option'

A'{"name":"John"}'

Berr

C'error'

D'data'

Attempts:

3 left

💡 Hint

Common Mistakes

Using invalid JSON string in the first blank.

Using wrong parameter name in catch block.

Emitting a wrong event name instead of 'error'.

The JSON.parse method parses a JSON string. The catch block catches the error as err and emits an 'error' event with it.