Error handling on client in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the GraphQL response has errors.

GraphQL

if (response.[1]) {
  console.log('Error found');
}

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

Adata

Bstatus

Cresult

Derrors

Attempts:

3 left

💡 Hint

Common Mistakes

Checking the 'data' field instead of 'errors'.

Using 'status' which is not part of GraphQL response object.

The errors field in a GraphQL response indicates if there were any errors during the query.

2fill in blank

medium

Complete the code to extract error messages from the GraphQL response.

GraphQL

const messages = response.errors.map(error => error.[1]);

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

Amessage

Bcode

Cstatus

Ddetail

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'code' or 'status' which are not standard error properties.

Trying to access 'detail' which is not part of GraphQL error objects.

The message property contains the human-readable error message in each error object.

3fill in blank

hard

Fix the error in the code to properly handle GraphQL errors in a try-catch block.

GraphQL

try {
  const response = await fetchGraphQL(query);
  if (response.[1]) {
    throw new Error('GraphQL error');
  }
} catch (error) {
  console.error(error);
}

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

Adata

Bstatus

Cerrors

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Checking 'data' instead of 'errors'.

Checking 'status' which is not part of the GraphQL response.

Checking response.errors is the correct way to detect GraphQL errors before throwing.

4fill in blank

hard

Fill both blanks to log all error messages from the GraphQL response.

GraphQL

if (response.[1]) {
  response.errors.forEach(error => {
    console.log(error.[2]);
  });
}

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

Aerrors

Bmessage

Cdata

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'data' or 'status' instead of 'errors' for the first blank.

Using 'status' or 'data' instead of 'message' for the second blank.

The errors field holds the error list, and each error's message contains the text.

5fill in blank

hard

Fill all three blanks to create a function that returns error messages from a GraphQL response or an empty array if none.

GraphQL

function getErrorMessages(response) {
  return response.[1] ? response.errors.map(error => error.[2]) : [3];
}

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

Aerrors

Bmessage

C[]

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Returning null instead of an empty array when no errors.

Using 'data' or 'status' instead of 'errors' for the first blank.

This function checks if errors exist, maps their message properties, or returns an empty array if no errors.

Practice

1. What is the main purpose of error handling on the client side in GraphQL applications?

easy

A. To speed up the server response time

B. To keep the app stable and show clear messages to users

C. To change the GraphQL schema dynamically

D. To store data permanently on the client

Solution

1. Step 1: Understand client-side error handling

   Error handling on the client is about managing problems that happen when fetching or processing data, so the app doesn't crash.

2. Step 2: Identify the main goal

   The goal is to keep the app stable and inform users clearly about what went wrong.

3. Final Answer:

   To keep the app stable and show clear messages to users -> Option B

4. Quick Check:

   Error handling = stability + clear messages [OK]

Hint: Error handling means stability and clear user messages [OK]

Common Mistakes:

• Thinking error handling speeds up server
• Confusing error handling with schema changes
• Assuming error handling stores data

2. Which of the following is the correct way to catch errors from a GraphQL query using promises on the client?

easy

A. client.query(...).then(...).catch(error => handleError(error))

B. client.query(...).catch(...).then(error => handleError(error))

C. client.query(...).try(error => handleError(error))

D. client.query(...).error(error => handleError(error))

Solution

1. Step 1: Recall promise error handling syntax

   Promises use .then() for success and .catch() for errors.

2. Step 2: Match correct chaining

   The correct order is .then(...).catch(...). client.query(...).then(...).catch(error => handleError(error)) matches this.

3. Final Answer:

   client.query(...).then(...).catch(error => handleError(error)) -> Option A

4. Quick Check:

   Promise catch method = .catch() [OK]

Hint: Use .then() before .catch() to handle errors [OK]

Common Mistakes:

• Placing .catch() before .then()
• Using non-existent .try() or .error() methods
• Ignoring promise chaining order

3. Given the following code snippet, what will be logged if the GraphQL query fails?

client.query({ query: GET_USER })
  .then(response => console.log('User:', response.data.user))
  .catch(error => console.log('Error:', error.message))

medium

A. User: undefined

B. No output

C. User: null

D. Error: [error message from server]

Solution

1. Step 1: Understand promise flow on failure

   If the query fails, the .catch() block runs, logging the error message.

2. Step 2: Identify logged output

   The console logs 'Error:' followed by the error message from the server.

3. Final Answer:

   Error: [error message from server] -> Option D

4. Quick Check:

   Failed query triggers .catch() logging error [OK]

Hint: Failed queries run .catch() logging error message [OK]

Common Mistakes:

• Assuming .then() runs on failure
• Expecting 'User: undefined' instead of error
• Thinking no output appears on error

4. Identify the error in this client-side GraphQL error handling code:

try {
  const response = await client.query({ query: GET_POSTS });
  console.log(response.data.posts);
} catch {
  console.log('Failed to fetch posts');
}

medium

A. client.query does not return a promise

B. Using await inside try block is invalid

C. Missing error parameter in catch block

D. console.log cannot be used inside catch

Solution

1. Step 1: Review try-catch syntax

   The catch block should include an error parameter to access error details.

2. Step 2: Identify missing error parameter

   The code uses catch { ... } without (error), preventing access to the error details.

3. Final Answer:

   Missing error parameter in catch block -> Option C

4. Quick Check:

   catch needs (error) parameter [OK]

Hint: Always include error parameter in catch block [OK]

Common Mistakes:

• Omitting error parameter in catch
• Thinking await is invalid in try
• Believing client.query is not a promise

5. You want to show a friendly message to users when a GraphQL mutation fails due to network issues. Which approach correctly handles this on the client?

async function submitData() {
  try {
    const result = await client.mutate({ mutation: ADD_ITEM, variables: { name: 'Book' } });
    console.log('Item added:', result.data.addItem.id);
  } catch (error) {
    if (error.networkError) {
      alert('Network problem, please try again later.');
    } else {
      alert('An error occurred.');
    }
  }
}

hard

A. This code correctly distinguishes network errors and shows messages

B. The catch block should not check error properties

C. Using alert is not allowed in error handling

D. await cannot be used with client.mutate

Solution

1. Step 1: Analyze error handling logic

   The catch block checks if the error is a network error and shows a specific message.

2. Step 2: Confirm correct usage of await and alerts

   Using await with client.mutate is valid, and alerts are acceptable for user messages.

3. Final Answer:

   This code correctly distinguishes network errors and shows messages -> Option A

4. Quick Check:

   Check error.networkError to show friendly messages [OK]

Hint: Check error.networkError to show specific messages [OK]

Common Mistakes:

• Ignoring networkError property in catch
• Thinking alerts are disallowed
• Misunderstanding await usage with mutate