React Suspense: Responsive

⚡️ Responsive Inputs with useDeferredValue: Making UX Smoother with React

Have you ever typed in a search input, only to feel it lag behind your keystrokes?

That’s not just annoying—it’s a broken user experience. Fortunately, React gives us tools to keep your inputs responsive even during async operations like data fetching.

Let’s dive into how you can use useDeferredValue to solve this problem.

🧩 The Problem: Laggy Search Inputs with useTransition

In earlier exercises (or maybe in your app), you may have used React’s useTransition to manage asynchronous rendering like this:

const [isPending, startTransition] = useTransition()

function handleChange(e) {
  const newValue = e.target.value
  startTransition(() => {
    setSearch(newValue)
  })
}

This works well for navigation or large UI changes because useTransition delays re-rendering of everything until it’s ready. It’s great for global UI transitions, but it introduces a serious problem in interactive components:

The input field doesn’t update as fast as the user types.

Why? Because React holds onto the previous state during the transition.

🧪 Try it:

• Type “Falcon”
• You’ll notice a slight delay before the input catches up
• That delay makes the input feel unresponsive 😩

This is where useDeferredValue shines. 🌟

✅ The Solution: useDeferredValue

useDeferredValue is a React Hook designed to keep inputs responsive while still supporting async rendering in components that depend on the state.

Here’s how it works:

const deferredValue = useDeferredValue(value)

React immediately renders the component with the latest value, and in the background, it renders it again with a deferred version of that value. When you’re fetching or rendering based on deferredValue, React can pause and resume rendering based on how fast or slow that operation is.

Example:

const [search, setSearch] = useState('')
const deferredSearch = useDeferredValue(search)

const results = use(searchShips(deferredSearch)) // Suspense-aware data fetching

Here’s what happens under the hood:

1. User types A → React sets search = "A"
2. Component re-renders immediately with search = "A"
3. Meanwhile, deferredSearch might still be "" for a brief moment
4. Once idle time is available, React renders again with deferredSearch = "A"

That small delay lets us keep the input responsive, even when data fetching suspends.

🧠 How It’s Different from useTransition

Both useTransition and useDeferredValue help manage suspended UIs, but they serve different goals:

Use useTransition for big transitions like routing.

Use useDeferredValue for granular interactivity like form input.

✨ Adding Pending UI with useDeferredValue

You can recreate a similar isPending experience like this:

const isPending = deferredSearch !== search

Then show a spinner or opacity animation:

{isPending && <LoadingSpinner />}

👨‍💻 Practical Code Example

function ShipSearch() {
  const [search, setSearch] = useState('')
  const deferredSearch = useDeferredValue(search)

  const ships = use(searchShips(deferredSearch)) // suspends while fetching
  const isPending = deferredSearch !== search

  return (
    <>
      <input
        type="text"
        value={search}
        onChange={(e) => setSearch(e.target.value)}
        placeholder="Search ships..."
      />
      {isPending && <span>Loading...</span>}
      <ul>
        {ships.map((ship) => (
          <li key={ship.id}>{ship.name}</li>
        ))}
      </ul>
    </>
  )
}

🔬 Debug It Yourself

To really see how this works:

1. Add a console.log('search', search, 'deferred', deferredSearch) inside your component.
2. Simulate a slow network: searchShips(search, 1000)
3. Watch how many renders React performs and in what order.

You’ll notice:

• One render happens right after typing
• Another follows shortly with the deferred value
• The UI remains responsive throughout 🟢

🧪 Bonus: Use useDeferredValue for Slow Components Too

If you have a slow-to-render component, pass it a deferred value. React will keep the rest of your UI snappy and only update the slow component when it’s ready.

<SlowComponent data={useDeferredValue(data)} />

This allows users to interact with other parts of your app without delay.

🧠 Recap

📘 Further Reading

• React Docs: useDeferredValue
• Suspense for Data Fetching

✍️ Final Thought

In a world where users expect instant feedback, even 100ms of delay can feel frustrating. With useDeferredValue, you can keep your UI buttery smooth—without sacrificing loading logic or async data handling.

Start small with search bars and inputs—and watch your UX transform. 🚀

Have a sluggish input component? Drop the code here and I’ll help you refactor it!