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Async UI & Complex Forms

Make every asynchronous operation and form workflow resilient to slow networks, rapid user input, out-of-order responses, interruptions and server errors.

1. Preventing stale responses and race conditions

• Whenever a user can trigger overlapping requests (typing in search boxes, switching tabs/filters rapidly, changing route params, clicking pagination), prevent an older slow response from overwriting a newer result:
  • Pass an AbortController signal to fetch / axios and call controller.abort() inside onWatcherCleanup (Vue 3.5+) or watch's onCleanup((_, __, onCleanup) => onCleanup(() => controller.abort())), and on unmount.
  • Or increment a local requestId counter before each request and ignore any response where currentId !== requestId before mutating reactive state (data, error, isLoading).
• Ignore AbortError when setting user-facing error state so canceled requests never flash an error banner.

2. Explicit async UI states

• Model async status explicitly (idle, loading, error, success) rather than ambiguous booleans that allow contradictory states (such as showing both an error banner and a loading spinner or a flash of "No items found" before the first request starts).
• Distinguish initial load (skeleton matching the layout) from background refresh / filter update (keep existing data visible with aria-busy="true" or a subtle progress indicator instead of blanking the screen).
• On error, preserve the user's input, explain what failed clearly, and offer a working retry or recovery action.

3. Double-submit protection, retries and optimistic UI

• Guard every mutation action against double clicks or repeated Enter presses:
  • Check if (isSubmitting.value) return at the start of the handler, set isSubmitting.value = true in try, and reset in finally.
  • Disable or mark the submit control busy while in flight.
• For optimistic updates (toggles, reordering, quick deletes), snapshot the previous state before applying the optimistic mutation, roll back to the snapshot if the request fails, and show a clear error toast.

4. Complex, dynamic and multi-step forms

• Give dynamic form array rows (line items,repeater fields) a stable unique id generated at row creation (crypto.randomUUID() or counter) for :key — never :key="index", which corrupts field state and validation errors when rows are inserted or removed.
• Separate field-level validation timing: validate eagerly only after a field has been blurred (touched) or after the first submit attempt, and clear a field's error as soon as the user corrects it.
• Map server-side field validation errors (422) back onto the corresponding fields, open the step/tab containing the first invalid field in multi-step forms, and move focus to the first invalid input (aria-invalid="true", aria-describedby).
• Track dirty state against the initial snapshot so Cancel, modal close or route leave warns before losing unsaved work.

Before you finish

• Rapid filter/tab/param changes cancel or ignore stale responses via AbortController or request tokens.
• Mutations block duplicate submissions while in flight and preserve user input when a request fails.
• Dynamic form rows use stable unique keys, and server/client validation errors link to fields and focus the first invalid control.
• Loading, empty, error, retry and dirty-leave states all work predictably.