Mastering useDeferredValue: Enhancing UI Responsiveness in React

Some React operations are expensive: rendering large lists, filtering big datasets, working through heavy UI components. Update the whole component immediately on every keystroke and the UI starts to feel sluggish.

The useDeferredValue hook addresses this issue by delaying non-urgent updates in a component and prioritizing more critical interactions, ensuring the app remains responsive.

Syntax

const deferredValue = useDeferredValue(value)

• **value**: The value you want to defer. When this value changes, React won’t update the UI immediately but will instead render the new value later.
• **deferredValue**: This is the deferred version of the original value. It will lag behind value until React has finished processing higher-priority updates.

Understanding How Deferred Values Work ⭐

On the initial render, useDeferredValue returns the same value you handed it. Nothing clever yet. On subsequent updates React first returns the previous value to keep the UI responsive, then schedules a background re-render to catch the component up to the new value (assuming there is one).

Usage

Call useDeferredValue at the top level of the component to get a deferred version of a value. It earns its keep when the value drives an expensive computation or render and updates frequently — text search being the canonical case:

import { useState, useDeferredValue } from 'react'  
  
function MyComponent() {  
  const [state, setState] = useState('')  
  const deferredQuery = useDeferredValue(state)  
  // ...  
}

Using useDeferredValue in Conjunction With a Suspense

Two ways to show a fallback UI during an expensive render:

1. Not showing anything while rendering
2. Keeping on showing the previous results until new results become ready

The first is simpler and doesn’t require a deferred value. A state variable plus a Suspense boundary is enough to suspend the component while it renders:

import { Suspense, useState } from 'react'  
import SearchResults from './SearchResults.js'  
  
export default function App() {  
  const [query, setQuery] = useState('')  
  return (  
    <div>  
      <label>  
        Search:  
        <input value={query} onChange={e => setQuery(e.target.value)} />  
      </label>  
      <Suspense fallback={<h2>Loading...</h2>}>  
        <SearchResults query={query} />  
      </Suspense>  
    </div>  
  )  
}

If instead you want to keep the “previous results” on screen while the new ones load, hand the deferred value to the child component inside the Suspense boundary.

import { Suspense, useState, useDeferredValue } from 'react'  
import SearchResults from './SearchResults.js'  
  
export default function App() {  
  const [query, setQuery] = useState('')  
  const deferredQuery = useDeferredValue(query)  
  return (  
    <>  
      <label>  
        Search albums:  
        <input value={query} onChange={e => setQuery(e.target.value)} />  
      </label>  
      <Suspense fallback={<h2>Loading...</h2>}>  
        <SearchResults query={deferredQuery} />  
      </Suspense>  
    </>  
  )  
}

Passing the deferred version of the query keeps SearchResults rendering the old results until the new ones are ready.

💡 Assuming the data fetch in SearchResults component is happening in an effect, passing the query (or deferredQuery) as a dependency to the effect would prevent unnecessary network requests.

Caveats

• Deferring a value whose update is already inside a useTransition buys you nothing — useDeferredValue won’t pile a second defer on top of a transition.
• Pass useDeferredValue a primitive (string, number) or an object created outside of rendering (memoized values, state variables). More on why in the referential-equality section below.
• The background rendering of the deferred value can be interrupted by other updates to the value, in which case React restarts the rendering with the newest value.
• There’s no fixed delay. The moment the original re-render finishes, React picks up the background one.
• The background re-render caused by useDeferredValue does not fire Effects until the changes are reflected to the UI.

Common Pitfalls and Best Practices

1. Don’t defer everything: useDeferredValue helps when something is actually slow. Reach for it when you can measure the jank, not preemptively.
2. Don’t defer feedback users are waiting on: text inputs, form fields, anything the user expects to see react instantly. Deferring those feels broken.
3. Save it for the heavy stuff: filtering, sorting and rendering large lists. Lightweight updates don’t need it and you’ll only add complexity.

Differences Between useDeferredValue and useTransition

Both useTransition and useDeferredValue defer updates, so where’s the line?

• **useTransition**: Allows you to mark a state update as low-priority, deferring the rendering of the state change (like updating a list or complex UI elements). It’s often used when you want to handle multiple updates at once and prioritize certain updates over the others.
• **useDeferredValue**: Specifically defers a value (which could be a state variable, a memoized object, or a primitive value). When the value gets updated, React delays the rendering of that change in favor of more urgent updates (like input handling).

Regarding Referential Equality

The values you pass into useDeferredValue should be either primitive values (e.g., strings and numbers) or objects that are created outside of rendering.

This trips people up a lot, and it matters beyond useDeferredValue — the same gotcha shows up across the hook API.

Every re-render runs the component function again, so anything declared inside the function body is a fresh object. For example:

function MyComponent({ data }) {  
  const obj = { key: "value" } // this object gets re-created on each render  
  const deferredObj = useDeferredValue(obj)  
  return <div>{deferredObj.key}</div>  
}

React decides whether a value changed by comparing references with Object.is. Objects and arrays created inline are fresh on every render, so React sees them as new each time. With useDeferredValue that means wasted background renders and the perf win you reached for evaporates.

Avoiding Referential Equality Problems

To dodge the referential-equality trap, the objects and arrays you pass into React hooks need to be stable across renders. A handful of options:

• **useMemo**: Memoizes an object or array so that it only gets recreated if its dependencies change. This way, the object maintains a stable reference between renders.
• **useState**: State values are managed by React and are stable across renders unless explicitly updated through the state setter functions.
• Primitive values: Primitive values like strings, numbers, booleans, null, and undefined behave differently than objects and arrays in JavaScript when it comes to equality. Primitive values are compared by value, not by reference, so they do not cause referential equality problems in the same way that objects and arrays do.

So in our example, to give the object a stable identity we can either wrap it in useMemo or stash it in useState:

Stabilizing a Value With useMemo

function MyComponent() {  
  const obj = useMemo(() => ({ key: 'value' }), []) // memoizing the object to ensure referential equality  
  const deferredObj = useDeferredValue(obj)  
  return <div>{deferredObj.key}</div>  
}

Stabilizing a Value With useState

function MyComponent() {  
  const [obj, setObj] = useState({ key: 'value' }) // using a state variable to ensure referential equality  
  const deferredObj = useDeferredValue(obj)  
  return <div>{deferredObj.key}</div>  
}