Suspense for async components in Vue - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of <Suspense> in Vue?

The <Suspense> component lets Vue show a fallback UI while waiting for async components or async setup to finish loading. It improves user experience by showing a loading state instead of a blank screen.

beginner

How do you define an async component in Vue to use with <Suspense>?

You define an async component by using defineAsyncComponent or a dynamic import. For example: const AsyncComp = defineAsyncComponent(() => import('./MyComponent.vue')).

intermediate

What happens if an async component inside <Suspense> fails to load?

If an async component fails to load, <Suspense> can show an error fallback if provided, or the error will propagate. You can handle errors by using errorCaptured lifecycle hook or error slots in <Suspense>.

intermediate

Can <Suspense> handle multiple async components at once?

Yes, <Suspense> waits for all async components inside it to resolve before showing the main content. Until then, it shows the fallback UI.

beginner

What is the role of the fallback slot in <Suspense>?

The fallback slot defines what the user sees while async components are loading. It usually contains a loading spinner or message to indicate progress.

What does the <Suspense> component show while waiting for async components?

A The fallback slot content

B The main component content

C An error message

D Nothing, it stays blank

shows the fallback slot content while async components are loading.

How do you create an async component in Vue to use with <Suspense>?

A Using a computed property

B Using v-if directive

C Using a synchronous import

D Using defineAsyncComponent or dynamic import

Async components are created with defineAsyncComponent or dynamic import to load them lazily.

If multiple async components are inside one <Suspense>, when does it show the main content?

A Never, it always shows fallback

B After the first async component loads

C After all async components finish loading

D Immediately without waiting

waits for all async components inside it to resolve before showing main content.

What slot do you use inside <Suspense> to show a loading spinner?

A error

B fallback

C default

D loading

The fallback slot is used to show loading UI while waiting for async components.

How can you handle errors from async components inside <Suspense>?

A Using errorCaptured hook or error slot

B Using v-show directive

C Using a try-catch block in template

D You cannot handle errors in <Suspense>

Errors can be handled with errorCaptured lifecycle hook or error slot inside .

Explain how improves user experience when loading async components in Vue.

Think about what users see during loading.

Describe how to define and use an async component with in Vue.

Focus on component creation and template usage.

Practice

1. What is the main purpose of the <Suspense> component in Vue?

easy

A. To show fallback content while async components are loading

B. To handle errors in synchronous components

C. To style components with CSS

D. To manage global state across components

Solution

1. Step 1: Understand what async components do

   Async components load their code or data asynchronously, which can take some time.

2. Step 2: Role of <Suspense>

   The <Suspense> component shows fallback content during this loading time to improve user experience.

3. Final Answer:

   To show fallback content while async components are loading -> Option A

4. Quick Check:

   Suspense = fallback content during loading [OK]

Hint: Suspense shows a placeholder while waiting for async parts [OK]

Common Mistakes:

• Confusing Suspense with error handling
• Thinking Suspense manages CSS or styling
• Assuming Suspense manages global state

2. Which of the following is the correct way to use <Suspense> with a fallback in Vue?

easy

A. <Suspense><AsyncComp /><template fallback>Loading...</template></Suspense>

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

C. <Suspense><template #fallback>Loading...</template><AsyncComp /></Suspense>

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

Solution

1. Step 1: Check Vue Suspense syntax

   Vue uses a named slot #fallback inside <Suspense> to show fallback content.

2. Step 2: Validate the options

   <Suspense><template #fallback>Loading...</template><AsyncComp /></Suspense> correctly uses <template #fallback> with fallback text and wraps the async component inside Suspense.

3. Final Answer:

   <Suspense><template #fallback>Loading...</template><AsyncComp /></Suspense> -> Option C

4. Quick Check:

   Fallback slot syntax = <Suspense><template #fallback>Loading...</template><AsyncComp /></Suspense> [OK]

Hint: Use inside Suspense for fallback content [OK]

Common Mistakes:

• Trying to pass fallback as a prop
• Placing fallback template after async component
• Using incorrect slot name like 'fallback' without #

3. Given this Vue template:

<Suspense>
  <template #fallback>Loading...</template>
  <AsyncUser />
</Suspense>

What will the user see while AsyncUser is loading?

medium

A. The AsyncUser component will show partial content

B. Nothing will be shown until AsyncUser loads

C. An error message will appear

D. The text 'Loading...' will be shown

Solution

1. Step 1: Understand Suspense fallback behavior

   While the async component is loading, the fallback slot content is displayed.

2. Step 2: Identify fallback content

   The fallback slot contains the text 'Loading...', so this text appears during loading.

3. Final Answer:

   The text 'Loading...' will be shown -> Option D

4. Quick Check:

   Fallback slot content shows during loading = The text 'Loading...' will be shown [OK]

Hint: Fallback slot content appears while async component loads [OK]

Common Mistakes:

• Expecting no content during loading
• Thinking partial async component renders
• Confusing fallback with error message

4. What is wrong with this Vue Suspense usage?

<Suspense>
  <AsyncComp />
  <template fallback>Loading...</template>
</Suspense>

medium

A. Fallback content must be a component, not a template

B. The fallback template must use #fallback slot syntax

C. Suspense cannot wrap async components

D. AsyncComp must be wrapped in a div

Solution

1. Step 1: Check fallback slot syntax

   The fallback slot requires the named slot syntax #fallback inside <template>.

2. Step 2: Identify the error in code

   The code uses <template fallback> instead of <template #fallback>, which is invalid.

3. Final Answer:

   The fallback template must use #fallback slot syntax -> Option B

4. Quick Check:

   Fallback slot needs #fallback syntax = The fallback template must use #fallback slot syntax [OK]

Hint: Use not for fallback slot [OK]

Common Mistakes:

• Omitting the # in fallback slot
• Wrapping async component unnecessarily
• Thinking fallback must be a separate component

5. You want to show a loading spinner while two async components load in parallel inside Suspense. Which approach correctly shows fallback until both finish loading?

hard

A. <Suspense><template #fallback><Spinner /></template><AsyncComp1 /><AsyncComp2 /></Suspense>

B. <Suspense><AsyncComp1 /><template fallback><Spinner /></template><AsyncComp2 /></Suspense>

C. <Suspense><AsyncComp1 /><AsyncComp2 /></Suspense><template #fallback><Spinner /></template>

D. <Suspense><template #fallback><Spinner /></template><AsyncComp1 /></Suspense><Suspense><template #fallback><Spinner /></template><AsyncComp2 /></Suspense>

Solution

1. Step 1: Understand Suspense behavior with multiple async components

   A single Suspense wrapping multiple async components waits for all to load before showing content.

2. Step 2: Check fallback placement

   The fallback slot must be declared once inside Suspense before the async components to show fallback while any are loading.

3. Final Answer:

   <Suspense><template #fallback><Spinner /></template><AsyncComp1 /><AsyncComp2 /></Suspense> -> Option A

4. Quick Check:

   Single Suspense with fallback wraps all async components = <Suspense><template #fallback><Spinner /></template><AsyncComp1 /><AsyncComp2 /></Suspense> [OK]

Hint: Wrap all async components in one Suspense with fallback slot [OK]

Common Mistakes:

• Placing fallback after async components
• Using multiple Suspense components separately
• Putting fallback outside Suspense