Error-first callback convention in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a callback that handles an error first.

Node.js

function callback([1], data) {
  if ([1]) {
    console.error('Error:', [1]);
  } else {
    console.log('Data:', data);
  }
}

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

Aerror

Bresult

Cresponse

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using the data argument as the first parameter instead of the error.

Naming the first argument something unrelated like 'result'.

The first argument in an error-first callback is the error object, commonly named error.

2fill in blank

medium

Complete the code to call the callback with an error.

Node.js

function fetchData(callback) {
  const error = new Error('Failed to fetch');
  callback([1], null);
}

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

Aundefined

Bnull

Cerror

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Passing null as the first argument when there is an error.

Passing false or undefined instead of the error object.

When there is an error, the first argument to the callback should be the error object.

3fill in blank

hard

Fix the error in the callback usage to follow the error-first convention.

Node.js

function processData(callback) {
  const data = { value: 42 };
  callback([1]);
}

processData(function(err, data) {
  if (err) {
    console.error(err);
  } else {
    console.log(data.value);
  }
});

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

Anull, data

Bdata

Cundefined

Ddata, null

Attempts:

3 left

💡 Hint

Common Mistakes

Passing data as the first argument instead of the second.

Omitting the second argument when there is no error.

The callback should be called with null as the first argument to indicate no error, and the data as the second argument.

4fill in blank

hard

Fill both blanks to create an error-first callback that logs error or success message.

Node.js

function handleResult([1], [2]) {
  if ([1]) {
    console.log('Error occurred:', [1]);
  } else {
    console.log('Success:', [2]);
  }
}

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

Aerr

Berror

Cresult

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of error and data parameters.

Using inconsistent variable names.

The first parameter is the error (named error), and the second is the data (named data).

5fill in blank

hard

Fill all three blanks to define a function that calls a callback with error or data properly.

Node.js

function getUser(id, [1]) {
  if (id <= 0) {
    [1](new Error('Invalid ID'), null);
  } else {
    const user = { id: id, name: 'Alice' };
    [1](null, [2]);
  }
}

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

Acallback

Buser

Cdata

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the callback parameter.

Passing wrong variables to the callback.

The function uses callback as the callback name. It calls callback with an error or with user data.