Suspense for async components in Vue - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Vue Suspense component render initially?

Consider this Vue 3 component using <Suspense> with an async child component. What will the user see first when this component is mounted?

Vue

<template>
  <Suspense>
    <template #default>
      <AsyncChild />
    </template>
    <template #fallback>
      <p>Loading...</p>
    </template>
  </Suspense>
</template>

<script setup>
import { defineAsyncComponent } from 'vue'

const AsyncChild = defineAsyncComponent(() =>
  new Promise(resolve => {
    setTimeout(() => {
      resolve({ template: '<p>Async content loaded</p>' })
    }, 2000)
  })
)
</script>

A The text 'Loading...' is shown immediately, then replaced by 'Async content loaded' after 2 seconds.

B The text 'Async content loaded' appears immediately without delay.

C Nothing is shown until the async component finishes loading after 2 seconds.

D An error message is displayed because async components cannot be used inside Suspense.

💡 Hint

Think about what the fallback slot in <Suspense> is for.

The <Suspense> component shows the fallback content immediately while waiting for the async component to load. Once loaded, it replaces the fallback with the async component's content.

❓ state_output

intermediate

What is the value of isPending during async component loading?

In Vue 3, when using defineAsyncComponent with Suspense, you can track loading state with isPending. What is the value of isPending while the async component is still loading?

Vue

<script setup>
import { defineAsyncComponent, ref } from 'vue'

const isPending = ref(false)

const AsyncComp = defineAsyncComponent({
  loader: () => new Promise(resolve => setTimeout(() => resolve({ template: '<p>Done</p>' }), 3000)),
  onPending() { isPending.value = true },
  onResolve() { isPending.value = false }
})
</script>

A null

B false

C undefined

D true

💡 Hint

Check what onPending does in defineAsyncComponent.

The onPending hook sets isPending to true when the async component starts loading. It stays true until the component resolves.

📝 Syntax

advanced

Which option correctly uses Suspense with multiple async components?

Given two async components AsyncA and AsyncB, which code snippet correctly uses <Suspense> to show a fallback while both load?

A

<Suspense>
  <template #default>
    <AsyncA />
    <AsyncB />
  </template>
  <template #fallback>
    <p>Loading both components...</p>
  </template>
</Suspense>

B

<Suspense>
  <AsyncA />
  <AsyncB />
  <template #fallback>
    <p>Loading both components...</p>
  </template>
</Suspense>

C

<Suspense fallback="<p>Loading both components...</p>">
  <AsyncA />
  <AsyncB />
</Suspense>

D

<Suspense>
  <template #fallback>
    <p>Loading both components...</p>
  </template>
  <AsyncA />
  <AsyncB />
</Suspense>

💡 Hint

Remember the correct slot names for Suspense fallback and default content.

The <Suspense> component requires the fallback content inside a named slot #fallback and the async components inside the default slot. Option A correctly uses both slots.

🔧 Debug

advanced

Why does this Suspense fallback never show?

Look at this Vue 3 code. The fallback slot content never appears even though the async component takes 3 seconds to load. Why?

Vue

<template>
  <Suspense>
    <AsyncComponent />
    <template #fallback>
      <p>Loading...</p>
    </template>
  </Suspense>
</template>

<script setup>
import { defineAsyncComponent } from 'vue'

const AsyncComponent = defineAsyncComponent(() =>
  new Promise(resolve => setTimeout(() => resolve({ template: '<p>Loaded</p>' }), 3000))
)
</script>

A The async component loads instantly, so fallback never shows.

B The fallback slot is ignored because the async component is not inside a default slot template.

C The fallback slot must be declared before the async component inside Suspense.

D Suspense requires a <SuspenseBoundary> wrapper to show fallback.

💡 Hint

Check how slots are structured inside Suspense.

Suspense expects async components inside the default slot. Here, <AsyncComponent /> is a direct child, not inside a <template #default>. So fallback is ignored and async component renders immediately when ready.

🧠 Conceptual

expert

How does Vue Suspense handle multiple async dependencies internally?

When a Vue Suspense component wraps multiple async components, how does it decide when to switch from fallback to default content?

A It renders each async component as soon as it resolves, replacing fallback piece by piece.

B It shows fallback until the first async component resolves, then switches to default content immediately.

C It waits for all async components inside the default slot to resolve before rendering the default content.

D It randomly picks one async component to wait for before switching from fallback.

💡 Hint

Think about the user experience when multiple async components load.

Vue Suspense waits for all async components inside the default slot to finish loading before replacing the fallback with the full default content. This ensures a smooth transition without partial content flashes.