Unsubscribing in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does unsubscribing mean in GraphQL subscriptions?

Unsubscribing means stopping the live updates from a GraphQL subscription. It tells the server you no longer want to receive data changes.

beginner

How do you unsubscribe from a GraphQL subscription in client code?

You call the unsubscribe() method on the subscription object returned when you start the subscription.

intermediate

Why is unsubscribing important in GraphQL subscriptions?

Unsubscribing frees up resources on both client and server. It stops unnecessary data flow and saves bandwidth and memory.

intermediate

What happens if you don't unsubscribe from a GraphQL subscription?

The subscription stays active, and the client keeps receiving updates. This can cause wasted resources and slow performance.

beginner

Show a simple example of unsubscribing from a GraphQL subscription using JavaScript.

const subscription = client.subscribe({ query: MY_SUBSCRIPTION }).subscribe({
  next(data) { console.log(data); },
  error(err) { console.error(err); }
});

// Later when you want to stop:
subscription.unsubscribe();

What method do you call to stop receiving updates from a GraphQL subscription?

A stop()

B unsubscribe()

C cancel()

D end()

The correct method to stop a subscription is unsubscribe().

Why should you unsubscribe from a GraphQL subscription when no longer needed?

A To increase data flow

B To restart the subscription automatically

C To save server and client resources

D To change the subscription query

Unsubscribing saves resources by stopping unnecessary data updates.

If you forget to unsubscribe, what is a likely consequence?

A You keep receiving updates and waste resources

B The subscription stops automatically

C The server disconnects the client

D The client crashes immediately

Without unsubscribing, updates continue and resources are wasted.

In JavaScript, what does the subscribe() method return?

A A promise

B A boolean value

C A string token

D An object with an unsubscribe() method

subscribe() returns an object that has an unsubscribe() method to stop updates.

Which of these is NOT a reason to unsubscribe?

A To keep receiving data

B To reduce network traffic

C To prevent memory leaks

D To improve app performance

Unsubscribing stops data flow, so keeping data means not unsubscribing.

Explain what unsubscribing means in GraphQL subscriptions and why it is important.

Think about stopping live updates and saving resources.

Describe how you unsubscribe from a GraphQL subscription in client code with an example.

Focus on the object returned by subscribe() and its method.

Practice

1.

What does calling unsubscribe() on a GraphQL subscription do?

easy

A. It pauses the subscription but keeps the connection alive.

B. It restarts the subscription to receive updates again.

C. It deletes the subscription from the server permanently.

D. It stops receiving live updates from the subscription.

Solution

1. Step 1: Understand the purpose of unsubscribe()

   The unsubscribe() method is designed to stop live updates from a GraphQL subscription.

2. Step 2: Differentiate from other actions

   It does not restart, delete permanently, or pause the subscription; it simply stops updates.

3. Final Answer:

   It stops receiving live updates from the subscription. -> Option D

4. Quick Check:

   Unsubscribe() stops updates = D [OK]

Hint: Remember: unsubscribe() means stop updates completely [OK]

Common Mistakes:

• Thinking unsubscribe() restarts the subscription
• Confusing unsubscribe() with deleting the subscription
• Assuming unsubscribe() only pauses updates

2.

Which of the following is the correct syntax to stop a GraphQL subscription stored in variable sub?

const sub = client.subscribe({ query: MY_SUBSCRIPTION });
// Stop subscription here

easy

A. sub.stop();

B. unsubscribe(sub);

C. sub.unsubscribe();

D. client.unsubscribe(sub);

Solution

1. Step 1: Identify the unsubscribe method on subscription object

   The subscription object returned by client.subscribe() has an unsubscribe() method to stop it.

2. Step 2: Match correct syntax

   Calling sub.unsubscribe(); correctly stops the subscription. Other options are invalid method calls.

3. Final Answer:

   sub.unsubscribe(); -> Option C

4. Quick Check:

   Call unsubscribe() on subscription object = A [OK]

Hint: Use unsubscribe() method on the subscription variable [OK]

Common Mistakes:

• Using unsubscribe() as a standalone function
• Calling stop() instead of unsubscribe()
• Trying to unsubscribe via client object

3.

Given the code below, what will be logged after sub.unsubscribe() is called?

const sub = client.subscribe({ query: MY_SUBSCRIPTION });
sub.subscribe({
  next(data) { console.log('Received:', data); },
  error(err) { console.error('Error:', err); }
});

sub.unsubscribe();

// Later, server sends new data

medium

A. An error will be logged because subscription is closed.

B. No logs will appear after unsubscribe is called.

C. Logs will continue showing 'Received:' with new data.

D. Logs will show 'Received:' once more then stop.

Solution

1. Step 1: Understand unsubscribe effect on subscription callbacks

   Calling unsubscribe() stops the subscription and prevents further next callbacks.

2. Step 2: Predict logging behavior after unsubscribe

   Since subscription is stopped, no new data triggers console.log, so no logs appear after unsubscribe.

3. Final Answer:

   No logs will appear after unsubscribe is called. -> Option B

4. Quick Check:

   Unsubscribe stops callbacks = C [OK]

Hint: After unsubscribe, no more data callbacks occur [OK]

Common Mistakes:

• Expecting data logs after unsubscribe
• Assuming unsubscribe triggers an error
• Thinking one last data event logs after unsubscribe

4.

Identify the error in the code below that prevents unsubscribing correctly:

const subscription = client.subscribe({ query: NEW_MESSAGES });
subscription.next({
  next(data) { console.log(data); }
});

subscription.unsubscribe();

medium

A. Using subscription.next() instead of subscription.subscribe().

B. Calling unsubscribe() before subscribing.

C. Missing error callback in subscription.

D. Not assigning subscription to a variable.

Solution

1. Step 1: Check subscription method usage

   The subscription object uses subscribe() to listen for data, not next().

2. Step 2: Identify correct method to receive data

   Replacing subscription.next() with subscription.subscribe() fixes the issue and allows unsubscribe to work properly.

3. Final Answer:

   Using subscription.next() instead of subscription.subscribe(). -> Option A

4. Quick Check:

   Use subscribe(), not next(), to listen = B [OK]

Hint: Use subscribe() method to listen, not next() [OK]

Common Mistakes:

• Calling next() instead of subscribe()
• Unsubscribing before subscribing
• Ignoring error callback (not critical here)

5.

You have multiple active subscriptions stored in an array subs. How do you efficiently unsubscribe from all of them?

const subs = [sub1, sub2, sub3];
// Your code here

hard

A. subs.forEach(s => s.unsubscribe());

B. subs.unsubscribe();

C. for (let i = 0; i < subs.length; i++) { unsubscribe(subs[i]); }

D. subs.map(s => s.stop());

Solution

1. Step 1: Understand unsubscribing multiple subscriptions

   Each subscription object has an unsubscribe() method to stop it individually.

2. Step 2: Use array iteration to call unsubscribe on each

   Using subs.forEach(s => s.unsubscribe()); calls unsubscribe on all subscriptions efficiently.

3. Final Answer:

   subs.forEach(s => s.unsubscribe()); -> Option A

4. Quick Check:

   Call unsubscribe() on each subscription in array = A [OK]

Hint: Use forEach to unsubscribe all in array [OK]

Common Mistakes:

• Calling unsubscribe() on the array itself
• Using stop() method which does not exist
• Trying to call unsubscribe() without iteration