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fargo 1a822493ba format: apply repo prettier (3.8.1) to the folded skills tree

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2026-08-19 14:37:17 -05:00

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Suspense Fallback Not Immediately Shown on Revert

Rule

When Suspense reverts from resolved to pending state, the fallback content is NOT immediately displayed. Instead, the previous #default content remains visible while waiting for new content to resolve. Use the timeout prop to control when the fallback appears.

Why This Matters

This behavior prevents UI flicker for fast async operations, but can confuse users when loading takes longer than expected. Without understanding this, developers may think their fallback content is broken or Suspense isn't working correctly.

Bad Code

<template>
  <!-- Fallback won't show immediately when content changes -->
  <Suspense>
    <component :is="currentView" :key="viewKey" />

    <template #fallback>
      <!-- This may never appear for fast loads -->
      <LoadingSpinner />
    </template>
  </Suspense>
</template>

Good Code

Solution 1: Use timeout="0" for Immediate Fallback

<template>
  <!-- Fallback shows immediately on any pending state -->
  <Suspense timeout="0">
    <component :is="currentView" :key="viewKey" />

    <template #fallback>
      <LoadingSpinner />
    </template>
  </Suspense>
</template>

Solution 2: Use Appropriate Timeout for UX Balance

<template>
  <!-- Wait 200ms before showing fallback to avoid flicker on fast loads -->
  <Suspense :timeout="200">
    <component :is="currentView" :key="viewKey" />

    <template #fallback>
      <LoadingSpinner />
    </template>
  </Suspense>
</template>

Solution 3: Use Transitions for Smooth State Changes

<template>
  <RouterView v-slot="{ Component }">
    <template v-if="Component">
      <Transition mode="out-in">
        <Suspense :timeout="100">
          <component :is="Component" />

          <template #fallback>
            <div class="route-loading">
              <LoadingSpinner />
            </div>
          </template>
        </Suspense>
      </Transition>
    </template>
  </RouterView>
</template>

Timeout Behavior Summary

Timeout Value	Behavior
Not specified	Previous content shown until new content resolves (no fallback on revert)
`timeout="0"`	Fallback shown immediately when entering pending state
`timeout="200"`	Wait 200ms, then show fallback if still pending

When to Use Each Approach

No timeout (default):

When async operations are typically fast (<100ms)
When showing stale content is acceptable during loading
To prevent flicker on quick navigation

timeout="0":

When you always want to show loading feedback
For operations that typically take noticeable time
When stale content would be confusing

timeout with delay (e.g., 200ms):

Best of both worlds for most cases
Avoids flicker for fast loads
Still shows loading for slower operations

Key Points

Default Suspense behavior prioritizes showing stale content over fallback
Use timeout="0" if you always want the loading indicator
Choose timeout values based on expected async operation duration
Combine with <Transition> for smoother state changes
This behavior is by design to improve perceived performance

References

Vue.js Suspense Documentation

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