useTransition & useDeferredValue: The Future of Smooth UI in React


πŸ“… Published at: February 12, 2022

React 18 introduced two powerful hooksβ€”useTransition and useDeferredValueβ€”that help keep UIs responsive by preventing expensive renders from blocking urgent updates.

In this post, we’ll explore:
βœ… How useTransition and useDeferredValue work
βœ… When to use them for better performance
βœ… Real-world examples: search inputs, filtering large lists, and more


πŸš€ Why Does UI Lag Happen?

A common React problem is slow UI updates when performing expensive operations, such as:

  • Filtering a large list
  • Fetching & displaying API data
  • Rendering complex UI components

Without optimization, each keystroke in a search input could cause noticeable lag because React is synchronously updating state and rendering all filtered items immediately.

πŸ”Ή React 18 introduces useTransition() and useDeferredValue() to solve this.


1️⃣ useTransition(): Prioritizing UI Updates

What it does:

  • Allows React to split updates into urgent vs. non-urgent.
  • Keeps UI responsive by deferring slow updates until after urgent ones.

πŸ“Œ Example: Search Input Without useTransition() (Laggy UI)

Imagine a list of 10,000 items that updates on every keystroke:

import { useState } from "react";

function SearchList({ items }) {
  const [query, setQuery] = useState("");
  const [filteredItems, setFilteredItems] = useState(items);

  const handleSearch = (e) => {
    setQuery(e.target.value);
    setFilteredItems(items.filter(item => item.includes(e.target.value)));
  };

  return (
    <div>
      <input type="text" value={query} onChange={handleSearch} placeholder="Search..." />
      <ul>
        {filteredItems.map((item, index) => <li key={index}>{item}</li>)}
      </ul>
    </div>
  );
}

πŸ”΄ Problem: Every keystroke blocks the UI while filtering the list.


βœ… Optimized with useTransition() (Smooth UI)

import { useState, useTransition } from "react";

function SearchList({ items }) {
  const [query, setQuery] = useState("");
  const [filteredItems, setFilteredItems] = useState(items);
  const [isPending, startTransition] = useTransition();

  const handleSearch = (e) => {
    setQuery(e.target.value);
    startTransition(() => {
      setFilteredItems(items.filter(item => item.includes(e.target.value)));
    });
  };

  return (
    <div>
      <input type="text" value={query} onChange={handleSearch} placeholder="Search..." />
      {isPending && <p>Loading...</p>}
      <ul>
        {filteredItems.map((item, index) => <li key={index}>{item}</li>)}
      </ul>
    </div>
  );
}

βœ… How it helps:

  • Keystrokes update immediately (high priority).
  • Filtering runs in the background without blocking input.
  • UI remains responsive, even with large data sets.

2️⃣ useDeferredValue(): Deferring Expensive Computations

πŸ”Ή What it does:

  • Tells React to use the “stale” value until an expensive update is ready.
  • Unlike useTransition(), it doesn’t delay state updatesβ€”it delays how they propagate to children.

πŸ“Œ Example: Filtering a Large List Without useDeferredValue()

import { useState } from "react";

function SearchList({ items }) {
  const [query, setQuery] = useState("");

  // Expensive operation directly in render
  const filteredItems = items.filter(item => item.includes(query));

  return (
    <div>
      <input type="text" value={query} onChange={(e) => setQuery(e.target.value)} placeholder="Search..." />
      <ul>
        {filteredItems.map((item, index) => <li key={index}>{item}</li>)}
      </ul>
    </div>
  );
}

πŸ”΄ Problem:

  • Input lags on each keystroke as React recomputes the filtered list.

βœ… Optimized with useDeferredValue()

import { useState, useDeferredValue } from "react";

function SearchList({ items }) {
  const [query, setQuery] = useState("");
  const deferredQuery = useDeferredValue(query);

  // Filtering only updates when deferredQuery changes
  const filteredItems = items.filter(item => item.includes(deferredQuery));

  return (
    <div>
      <input type="text" value={query} onChange={(e) => setQuery(e.target.value)} placeholder="Search..." />
      <ul>
        {filteredItems.map((item, index) => <li key={index}>{item}</li>)}
      </ul>
    </div>
  );
}

βœ… How it helps:

  • Typing stays instant because filtering waits for deferredQuery to update.
  • UI updates without lag, keeping input interactions smooth.

πŸ›  When to Use useTransition() vs. useDeferredValue()?

FeatureuseTransition()useDeferredValue()
TypeHook for deferring state updatesHook for deferring computed values
PurposeSplits UI updates into urgent vs. non-urgentDelays expensive calculations to avoid UI blocking
Best Use CasesHandling async tasks, filtering large lists, rendering complex UIsLarge data sets, reducing unnecessary renders

πŸ’‘ Rule of thumb:

  • Use useTransition() when updating state directly affects UI.
  • Use useDeferredValue() when an expensive computation depends on a state value.

🎯 Real-World Use Cases

βœ… Filtering large lists efficiently (like search bars).
βœ… Debouncing slow UI updates without extra state management.
βœ… Rendering animations smoothly while loading new content.
βœ… Optimizing expensive calculations in dashboards and charts.


πŸ“Œ Final Thoughts

React 18’s useTransition() and useDeferredValue() give developers fine-grained control over rendering performance.

By prioritizing urgent updates and deferring expensive renders, you can:
βœ”οΈ Eliminate UI lag
βœ”οΈ Keep inputs fast & responsive
βœ”οΈ Improve perceived app performance


πŸ’‘ What’s Next?

πŸš€ Try implementing these hooks in your own project and see the difference!

πŸ’¬ Have you used useTransition() or useDeferredValue() yet? Let me know in the comments!


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