What does useDeferredValue() do?

ReactJunior~3 min read

What `useDeferredValue()` does

useDeferredValue() defers the update of some value, allowing React to first render urgent updates, and only then the "unhurried" ones.

Put simply: useDeferredValue() tells React: "Don't rush to update this value, do it when you have free time."

Syntax

javascript

const deferredValue = useDeferredValue(value);

value is a regular state value or variable;
deferredValue is the "deferred" version of that value, which updates a bit later, once React finishes the urgent renders.

Example: searching a large list

Without `useDeferredValue`

javascript

function Search({ data }) {
  const [query, setQuery] = useState("");

  const filtered = data.filter((item) => item.includes(query)); // heavy

  return (
    <>
      <input value={query} onChange={(e) => setQuery(e.target.value)} />
      <List items={filtered} />
    </>
  );
}

The problem:

Every character typed triggers filtering the whole collection.
The UI lags, there's a "lag" while typing.

With `useDeferredValue`

javascript

import { useDeferredValue } from "react";

function Search({ data }) {
  const [query, setQuery] = useState("");
  const deferredQuery = useDeferredValue(query); // defer the processing

  const filtered = data.filter((item) => item.includes(deferredQuery));

  return (
    <>
      <input value={query} onChange={(e) => setQuery(e.target.value)} />
      <List items={filtered} />
    </>
  );
}

What happens:

query updates immediately - the input field is responsive.
deferredQuery updates a bit later - React waits until the thread is free.
While filtering runs, you can even show a loading indicator.

Difference between `useTransition` and `useDeferredValue`

Feature	`useTransition`	`useDeferredValue`
What it does	Wraps a state update	A deferred version of a value
Used where	Where you call `setState`	Where you use the value
Returns	`[isPending, startTransition]`	`deferredValue`
Control	You decide yourself what to "defer"	React itself defers the update
Complexity	Need to wrap the logic	Very simple - 1 line

Essentially:

useTransition -> defers the action (setState).
useDeferredValue -> defers the result (value).

Example: filtering with a loading indicator

javascript

import { useDeferredValue } from "react";

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

  const filtered = items.filter((item) =>
    item.toLowerCase().includes(deferredQuery.toLowerCase())
  );

  const isStale = query !== deferredQuery; // the update hasn't caught up yet

  return (
    <>
      <input value={query} onChange={(e) => setQuery(e.target.value)} />
      {isStale && <p>Filtering...</p>}
      <List items={filtered} />
    </>
  );
}

Behavior:

While typing, the field reacts instantly.
Rendering the large list is slightly deferred.
"Filtering..." is shown while deferredQuery hasn't updated yet.

When to use `useDeferredValue()`

When	Why
Heavy filtering or sorting based on typed input	So typing doesn't lag
Rendering a large list or table	So rendering doesn't block the UI
The component receives an expensive prop value	So React doesn't recompute it instantly
You want a smooth update without the extra code of `useTransition`	It's a "shortcut" to the same goal

When you don't need to use it

Case	Why
Updates are light	React handles it fine anyway
There are no delays while typing	Excessive
An instant display is required	`useDeferredValue` is specifically not instant
For asynchronous requests	`useEffect` / `React Query` is better

Under the hood

useDeferredValue uses the same mechanism as startTransition: React marks the update as "not urgent" (low-priority). The difference is that:

you don't control it explicitly,
React decides itself when to catch the value up.

Summary

Question	Answer
What does `useDeferredValue()` do	Returns a deferred version of a value that updates with low priority
Why it's needed	To keep the interface responsive during heavy renders
When to use it	When rendering or computation depends on frequently updated state
When not to use it	If updates are light or must be instant
Analogy	Like `useTransition`, just "in one line"

Main idea:

useDeferredValue(value) -> "Don't update this value right away. Wait until the user stops actively interacting."

Short Answer

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