Data-fetching components handle loading, success, error, and empty states

Components that only handle the success path leave users stranded in three common failure modes: slow network (indefinite spinner), API error (blank or partially rendered page), and empty server response (no indication of why nothing appeared). CWE-703 (improper check for exceptional conditions) applies to missing error state handling. In vibe-coded applications this is one of the most frequent defects: AI code generation reliably handles the success path and omits the loading, error, and empty branches — leaving large surface areas completely unhandled.

Handle all four states explicitly in every data-fetching component. With TanStack Query or SWR, the state variables are provided; with raw useEffect, model them explicitly.

// components/item-list.tsx
export function ItemList() {
  const { data, isLoading, error } = useQuery({
    queryKey: ['items'],
    queryFn: fetchItems,
  })

  if (isLoading) return <Skeleton />
  if (error) return <ErrorMessage message="Failed to load items. Please refresh." />
  if (!data?.length) return <EmptyState message="No items yet." />
  return <ul>{data.map((item) => <li key={item.id}>{item.name}</li>)}</ul>
}

Do not conflate the error state with the empty state — an empty array is not an error, and an error is not an empty array.

• ID: data-fetching-states

• Severity: low

• What to look for: Count all data fetching hooks and components (useQuery, useSWR, fetch in useEffect). Enumerate which handle all 3 states (loading, error, success) vs. which only handle success. Examine components that fetch data (useEffect with fetch, async/await, React Query, SWR, etc.). Check whether they explicitly handle four states: loading (show spinner), success (show data), error (show error message), and empty (show empty state).

• Pass criteria: Data-fetching components explicitly handle all four states: loading, success, error, and empty. At least 90% of data fetching components must explicitly handle loading, error, and empty states.

• Fail criteria: Components lack explicit error state handling, or don't show empty state, or show loading indefinitely.

• Skip (N/A) when: The application has no data-fetching components.

• Do NOT pass when: Components handle error state by showing a loading spinner indefinitely instead of an actual error message.

• Cross-reference: For graceful API failure, see graceful-api-failure.

• Detail on fail: "Data-fetching components lack error state handling. Failed requests show blank screen" or "Loading state shown but no empty-state when API returns empty array"

• Remediation: Handle all four states:

  // components/user-list.tsx — all 3 data states
  if (isLoading) return <Skeleton />
  if (error) return <ErrorMessage message="Failed to load users" />
  if (!data.length) return <EmptyState message="No users found" />
  return <UserTable data={data} />
  

  export function ItemsList() {
    const [items, setItems] = useState([])
    const [loading, setLoading] = useState(true)
    const [error, setError] = useState(null)
  
    useEffect(() => {
      fetch('/api/items')
        .then(r => r.json())
        .then(data => {
          setItems(data)
          setError(null)
        })
        .catch(err => {
          setError(err)
          setItems([])
        })
        .finally(() => setLoading(false))
    }, [])
  
    if (loading) return <div>Loading...</div>
    if (error) return <div>Error: {error.message}</div>
    if (items.length === 0) return <div>No items found</div>
  
    return (
      <ul>
        {items.map(item => <li key={item.id}>{item.name}</li>)}
      </ul>
    )
  }