Streaming with Suspense in NextJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Suspense component from React.

NextJS

import { [1] } from 'react';

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

AFragment

BuseState

CSuspense

DuseEffect

Attempts:

3 left

💡 Hint

Common Mistakes

Importing useState instead of Suspense

Forgetting to import Suspense

Using Fragment which does not support fallback

The Suspense component is imported from React to enable streaming UI with fallback content.

2fill in blank

medium

Complete the code to wrap the component with Suspense and provide a fallback UI.

NextJS

<Suspense fallback=[1]>
  <Profile />
</Suspense>

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

Anull

B<ErrorBoundary />

C<div>Done</div>

D<LoadingSpinner />

Attempts:

3 left

💡 Hint

Common Mistakes

Using null as fallback which shows nothing

Using an error boundary as fallback which is incorrect

Using a static 'Done' message which does not indicate loading

The fallback prop shows a loading spinner while the Profile component is loading.

3fill in blank

hard

Fix the error in the code to correctly use Suspense with a lazy-loaded component.

NextJS

const LazyProfile = React.lazy(() => import('./Profile'));

export default function Page() {
  return (
    <Suspense [1]>
      <LazyProfile />
    </Suspense>
  );
}

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

Aloading={<Loading />}

Bfallback={<Loading />}

Cfallback={Loading}

Dfallback='Loading...'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'loading' instead of 'fallback' prop

Passing component reference without JSX brackets

Passing a string instead of a React element

The Suspense component requires a fallback prop with a React element to show while loading.

4fill in blank

hard

Fill both blanks to create a streaming component with Suspense and a loading fallback.

NextJS

export default function StreamPage() {
  return (
    <[1] [2]={<Spinner />}>
      <UserData />
    </[1]>
  );
}

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

ASuspense

Bfallback

Cloading

DErrorBoundary

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'loading' instead of 'fallback' prop

Using ErrorBoundary instead of Suspense

Forgetting to close the Suspense tag properly

Suspense wraps the UserData component and uses the fallback prop to show a spinner while loading.

5fill in blank

hard

Fill all three blanks to implement streaming with Suspense and a fallback loading message.

NextJS

import { [1] } from 'react';

const LazyComments = React.lazy(() => import('./Comments'));

export default function CommentsPage() {
  return (
    <[2] [3]={<p>Loading comments...</p>}>
      <LazyComments />
    </[2]>
  );
}

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

ASuspense

BuseState

Cfallback

Dloading

Attempts:

3 left

💡 Hint

Common Mistakes

Importing useState instead of Suspense

Using 'loading' instead of 'fallback' prop

Not wrapping LazyComments with Suspense

Suspense is imported and used to wrap LazyComments with a fallback prop showing a loading message.

Practice

1. What is the main purpose of using Suspense in Next.js streaming?

easy

A. To show a fallback UI while waiting for slow components to load

B. To prevent any component from rendering

C. To disable server-side rendering

D. To cache all components on the client

Solution

1. Step 1: Understand Suspense role

   Suspense is used to wrap components that may take time to load, showing a fallback UI meanwhile.

2. Step 2: Identify the purpose in streaming

   In streaming, it helps parts of the page appear quickly by showing placeholders until content is ready.

3. Final Answer:

   To show a fallback UI while waiting for slow components to load -> Option A

4. Quick Check:

   Suspense fallback = show UI while loading [OK]

Hint: Suspense shows fallback UI during loading [OK]

Common Mistakes:

• Thinking Suspense stops rendering completely
• Confusing Suspense with caching
• Assuming Suspense disables server rendering

2. Which of the following is the correct way to use Suspense in a Next.js component?

easy

A. <Suspense><MyComponent fallback="Loading..." /></Suspense>

B. <Suspense fallback="<Loading />"><MyComponent />

C. <Suspense fallback="Loading..."><MyComponent /></Suspense>

D. <Suspense fallback="<Loading />"><MyComponent /></Suspense>

Solution

1. Step 1: Check Suspense syntax

   The Suspense component requires a fallback prop with a React node, and must wrap the child component properly.

2. Step 2: Identify correct JSX structure

   <Suspense fallback="Loading..."><MyComponent /></Suspense> correctly uses fallback="Loading..." and properly closes the Suspense tag.

3. Final Answer:

   <Suspense fallback="Loading..."><MyComponent /></Suspense> -> Option C

4. Quick Check:

   Suspense fallback prop + proper closing = correct syntax [OK]

Hint: Suspense needs fallback prop and closing tag [OK]

Common Mistakes:

• Forgetting to close Suspense tag
• Passing fallback inside child component
• Using fallback as string with JSX tags

3. Given this Next.js component using streaming with Suspense:

import { Suspense } from 'react';

function SlowComponent() {
  return 
Data loaded
;
}

export default function Page() {
  return (
    

      Loading...
}>
        
      
    
  );
}

What will the user see first when this page loads?

medium

A. An error because Suspense cannot be used here

B. The text 'Loading...' immediately, then 'Data loaded' after SlowComponent finishes

C. A blank page until SlowComponent loads

D. Only 'Data loaded' without any loading text

Solution

1. Step 1: Check if SlowComponent suspends

   SlowComponent is synchronous and returns <div>Data loaded</div> immediately without throwing a promise, so Suspense does not trigger fallback.

2. Step 2: Determine initial render behavior

   The entire page renders instantly with 'Data loaded' inside the div. No fallback appears because there is no suspension.

3. Final Answer:

   Only 'Data loaded' without any loading text -> Option D

4. Quick Check:

   No suspend = no fallback, direct content render [OK]

Hint: Suspense fallback only if children suspend (throw promise) [OK]

Common Mistakes:

• Assuming Suspense always shows fallback
• Thinking synchronous components trigger loading
• Expecting streaming without suspend mechanism

4. Identify the error in this Next.js streaming code snippet:

import { Suspense } from 'react';

export default function Page() {
  return (
    <div>
      <Suspense fallback="Loading...">
        <SlowComponent />
      </Suspense>
    </div>
  );
}

function SlowComponent() {
  throw new Promise(resolve => setTimeout(resolve, 1000));
  return <div>Loaded</div>;
}

medium

A. The return statement after throw is unreachable

B. SlowComponent cannot throw a Promise

C. The fallback prop should be a React node, not a string

D. Suspense must be imported from 'next/suspense' not 'react'

Solution

1. Step 1: Spot unreachable code

   The return <div>Loaded</div> after throw is unreachable because the throw executes first.

2. Step 2: Validate other parts

   Import from 'react' is correct; throwing a Promise suspends correctly (though recreating it causes infinite loop here); fallback string is valid ReactNode.

3. Final Answer:

   The return statement after throw is unreachable -> Option A

4. Quick Check:

   throw before return = unreachable [OK]

Hint: Code after throw is unreachable [OK]

Common Mistakes:

• Thinking fallback string causes issues
• Believing components cannot throw Promises
• Wrong import source for Suspense

5. You want to stream two slow components in Next.js with Suspense, showing their fallbacks independently. Which approach correctly achieves this?

hard

A. <Suspense fallback="Loading..."><ComponentA /></Suspense><ComponentB fallback="Loading B..." />

B. <Suspense fallback="Loading A..."><ComponentA /></Suspense><Suspense fallback="Loading B..."><ComponentB /></Suspense>

C. <ComponentA /><ComponentB /> without Suspense

D. <Suspense fallback="Loading A and B..."><ComponentA /><ComponentB /></Suspense>

Solution

1. Step 1: Understand independent Suspense boundaries

   Wrapping each slow component in its own Suspense allows each to show its own fallback independently.

2. Step 2: Analyze options

   <Suspense fallback="Loading A..."><ComponentA /></Suspense><Suspense fallback="Loading B..."><ComponentB /></Suspense> wraps each component separately with distinct fallbacks, enabling independent streaming. <Suspense fallback="Loading A and B..."><ComponentA /><ComponentB /></Suspense> shares one fallback for both, so they load together. <ComponentA /><ComponentB /> without Suspense has no fallback. <Suspense fallback="Loading..."><ComponentA /></Suspense><ComponentB fallback="Loading B..." /> incorrectly uses fallback on a component.

3. Final Answer:

   <Suspense fallback="Loading A..."><ComponentA /></Suspense><Suspense fallback="Loading B..."><ComponentB /></Suspense> -> Option B

4. Quick Check:

   Separate Suspense per component = independent fallbacks [OK]

Hint: Wrap each slow component in its own Suspense [OK]

Common Mistakes:

• Using one Suspense for multiple components expecting separate fallbacks
• Not wrapping slow components in Suspense
• Passing fallback prop to child components