Optimistic UI updates in GraphQL - Mini Project: Build & Apply

Optimistic UI Updates with GraphQL

📖 Scenario: You are building a simple task management app where users can add tasks. To make the app feel fast, you want to show new tasks immediately in the UI before the server confirms the addition. This technique is called optimistic UI updates.

🎯 Goal: Create a GraphQL mutation setup that includes an optimistic response to update the UI instantly when adding a new task.

📋 What You'll Learn

Create a GraphQL mutation called ADD_TASK that adds a task with id and title fields.

Define a variable called newTask with id and title values.

Use an optimisticResponse object that matches the mutation shape with the newTask data.

Include the update function to update the cache with the new task.

💡 Why This Matters

🌍 Real World

Optimistic UI updates make apps feel faster by showing changes immediately without waiting for server confirmation.

💼 Career

Understanding optimistic updates is important for frontend developers working with GraphQL and Apollo Client to improve user experience.

1

Define the GraphQL mutation

Create a GraphQL mutation called ADD_TASK using the gql tag. The mutation should be named addTask and accept a title argument of type String!. It should return the id and title of the added task.

GraphQL

import { gql } from '@apollo/client';

// Define the ADD_TASK mutation
// Your code here

Hint

Use the gql tag to define a mutation named addTask that takes a title argument and returns id and title.

2

Create the new task variable

Create a constant variable called newTask with an id of "temp-id-1" and a title of "Learn optimistic UI".

GraphQL

import { gql } from '@apollo/client';

const ADD_TASK = gql`
  mutation addTask($title: String!) {
    addTask(title: $title) {
      id
      title
    }
  }
`;

// Create the newTask object
// Your code here

Hint

Define newTask as an object with the exact id and title values.

3

Add the optimisticResponse object

Create a constant called optimisticResponse that matches the mutation shape. It should have an addTask field containing the newTask object.

GraphQL

import { gql } from '@apollo/client';

const ADD_TASK = gql`
  mutation addTask($title: String!) {
    addTask(title: $title) {
      id
      title
    }
  }
`;

const newTask = {
  id: "temp-id-1",
  title: "Learn optimistic UI"
};

// Create optimisticResponse matching the mutation
// Your code here

Hint

The optimisticResponse object should have a field named addTask set to newTask.

4

Write the update function to modify the cache

Write a function called update that takes cache and { data: { addTask } } as parameters. Inside, call cache.modify to add addTask to the tasks field in the cache.

GraphQL

import { gql } from '@apollo/client';

const ADD_TASK = gql`
  mutation addTask($title: String!) {
    addTask(title: $title) {
      id
      title
    }
  }
`;

const newTask = {
  id: "temp-id-1",
  title: "Learn optimistic UI"
};

const optimisticResponse = {
  addTask: newTask
};

// Write the update function to add the new task to the cache
// Your code here

Hint

Use cache.modify to update the tasks field by appending the new task reference created with cache.writeFragment.

Practice

1. What is the main purpose of using optimisticResponse in GraphQL client updates?

easy

A. To show UI changes immediately before the server responds

B. To delay UI updates until the server confirms

C. To rollback UI changes after server response

D. To fetch data from the server without updating UI

Solution

1. Step 1: Understand optimisticResponse role

   The optimisticResponse is used to update the UI instantly, assuming the server will succeed.

2. Step 2: Compare options with purpose

   Only To show UI changes immediately before the server responds describes showing UI changes immediately before server confirmation, which matches the optimistic update concept.

3. Final Answer:

   To show UI changes immediately before the server responds -> Option A

4. Quick Check:

   optimisticResponse = immediate UI update [OK]

Hint: Think: optimistic means 'hopeful' update shown early [OK]

Common Mistakes:

• Confusing optimisticResponse with delayed updates
• Thinking it rolls back changes automatically
• Assuming it fetches data without UI change

2. Which of the following is the correct syntax to provide an optimistic response in a GraphQL mutation using Apollo Client?

easy

A. mutation({ variables, optimisticResponse: { id: 1, name: 'Test' } })

B. mutation({ variables, optimisticResponse: { __typename: 'User', id: 1, name: 'Test' } })

C. mutation({ variables, optimistic: { id: 1, name: 'Test' } })

D. mutation({ variables, optimisticResponse: { id: 1 } })

Solution

1. Step 1: Recall optimisticResponse structure

   The optimisticResponse must include the __typename field to match the GraphQL schema type.

2. Step 2: Check each option for __typename

   Only mutation({ variables, optimisticResponse: { __typename: 'User', id: 1, name: 'Test' } }) includes __typename: 'User' along with id and name, making it syntactically correct.

3. Final Answer:

   mutation({ variables, optimisticResponse: { __typename: 'User', id: 1, name: 'Test' } }) -> Option B

4. Quick Check:

   Include __typename in optimisticResponse [OK]

Hint: Always add __typename in optimisticResponse object [OK]

Common Mistakes:

• Omitting __typename causes errors
• Using 'optimistic' instead of 'optimisticResponse'
• Providing incomplete optimisticResponse data

3. Given this mutation call with optimisticResponse:

client.mutate({
  mutation: ADD_TODO,
  variables: { text: 'Buy milk' },
  optimisticResponse: {
    __typename: 'Mutation',
    addTodo: {
      __typename: 'Todo',
      id: 'temp-id',
      text: 'Buy milk',
      completed: false
    }
  }
})

What will the UI show immediately after this mutation is called but before the server responds?

medium

A. An error message about missing id

B. No change until server responds

C. A new todo with id 'temp-id' and text 'Buy milk' shown

D. A blank todo item with no text

Solution

1. Step 1: Analyze optimisticResponse content

   The optimisticResponse provides a new todo with id 'temp-id', text 'Buy milk', and completed false.

2. Step 2: Understand UI behavior

   The UI will immediately show this new todo item with the given fields before server confirmation.

3. Final Answer:

   A new todo with id 'temp-id' and text 'Buy milk' shown -> Option C

4. Quick Check:

   optimisticResponse shows temporary UI data [OK]

Hint: optimisticResponse data appears instantly in UI [OK]

Common Mistakes:

• Expecting no UI change before server response
• Thinking optimisticResponse causes errors
• Assuming blank or incomplete UI display

4. You wrote this optimisticResponse but the UI does not update immediately:

optimisticResponse: {
  addTodo: {
    id: 'temp-id',
    text: 'Buy milk',
    completed: false
  }
}

What is the most likely reason for this issue?

medium

A. optimisticResponse should be a function

B. Variables object is empty

C. Mutation name is incorrect

D. Missing __typename fields in optimisticResponse

Solution

1. Step 1: Check optimisticResponse structure

   The optimisticResponse must include __typename for each object to match the schema.

2. Step 2: Identify missing fields

   The given optimisticResponse lacks __typename fields, causing Apollo Client to ignore it.

3. Final Answer:

   Missing __typename fields in optimisticResponse -> Option D

4. Quick Check:

   __typename required for optimisticResponse to work [OK]

Hint: Always add __typename to every object in optimisticResponse [OK]

Common Mistakes:

• Forgetting __typename causes no UI update
• Assuming variables affect optimisticResponse directly
• Thinking optimisticResponse must be a function

5. You want to implement an optimistic UI update for a mutation that toggles a user's 'active' status. The server might reject the change. Which approach best ensures UI consistency?

hard

A. Use optimisticResponse to toggle status immediately and handle errors to revert if needed

B. Wait for server response before updating UI to avoid inconsistencies

C. Update UI without optimisticResponse and ignore server errors

D. Use optimisticResponse but do not handle errors, assuming success

Solution

1. Step 1: Understand optimistic UI with possible server rejection

   Optimistic UI shows changes immediately but must handle errors to keep UI correct.

2. Step 2: Evaluate options for best practice

   Use optimisticResponse to toggle status immediately and handle errors to revert if needed uses optimisticResponse for instant UI update and error handling to revert if server rejects, ensuring consistency.

3. Final Answer:

   Use optimisticResponse to toggle status immediately and handle errors to revert if needed -> Option A

4. Quick Check:

   Optimistic update + error handling = consistent UI [OK]

Hint: Combine optimisticResponse with error handling for safe UI [OK]

Common Mistakes:

• Ignoring error handling causes UI mismatch
• Waiting for server loses optimistic UI benefits
• Assuming optimisticResponse alone guarantees correctness