You have a search box. The user types react hooks, and your component fires an API request on every single keystroke — eleven requests for one query, ten of them already stale by the time they resolve. The fix everyone reaches for is debouncing: wait until the typing stops, then fire once. The fix everyone gets wrong is writing that debounce by hand with setTimeout inside a component, where stale closures, missing cleanup, and re-render churn quietly break it.
useDebounce is the hook that gets it right. This post covers the two shapes you actually need — debouncing a value and debouncing a callback — when to use each, and how to cancel or flush pending calls. Everything here is the real @reactuses/core API, SSR-safe and typed.
Why Not Just Use setTimeout?
Debouncing itself is simple: delay a function until a quiet period has passed, restarting the timer on every new call. (If you want the full conceptual breakdown — and how it differs from throttling — see Debounce vs Throttle in React.) The hard part is doing it inside a React component. Here is the naive version, and it has three bugs:
function Search() {
const (query, setQuery) = useState(”);
const timer = useRefReturnTypetypeof setTimeout>>();
function handleChange(e: React.ChangeEventHTMLInputElement>) {
const value = e.target.value;
setQuery(value);
clearTimeout(timer.current);
timer.current = setTimeout(() => {
fetchResults(value); // 🐛 see below
}, 300);
}
return input value={query} onChange={handleChange} />;
}
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It leaks on unmount. If the component unmounts while a timer is pending, the callback still fires 300 ms later — often setting state on a gone component, or hitting an API for a screen the user already left.
It captures stale values. The moment you debounce anything other than the raw event value — a second piece of state, a prop, a derived value — the closure freezes whatever those were when the timer was set, not when it fires.
It spreads. Every place that needs debouncing re-implements the useRef + clearTimeout dance, and each copy is a chance to forget the cleanup.
A hook fixes all three in one place. ReactUse ships two, built on the battle-tested lodash.debounce internally so the edge cases (leading edge, max wait, trailing edge) are already handled.
useDebounce — Debounce a Value
The most common case: you have a value that changes rapidly and you want a second, lagging copy of it that only updates after things settle. That second copy is what you feed into expensive work.
import { useState, useEffect } from ‘react’;
import { useDebounce } from ‘@reactuses/core’;
function Search() {
const (query, setQuery) = useState(”);
const debouncedQuery = useDebounce(query, 300);
useEffect(() => {
if (!debouncedQuery) return;
fetchResults(debouncedQuery);
}, (debouncedQuery));
return (
input
value={query}
onChange={(e) => setQuery(e.target.value)}
placeholder=”Search…”
/>
);
}
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The signature is useDebounce(value, wait?, options?) and it returns the debounced value, with the same type as the input:
const debounced = useDebounce(value, 300);
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The input (query) updates on every keystroke, so the controlled stays perfectly responsive — that’s the value you bind to the DOM. The output (debouncedQuery) only catches up 300 ms after the user stops typing, so it’s the value you put in the effect’s dependency array. The API fires once per pause instead of once per keystroke, and your input never feels laggy because the thing you typed into was never the thing being debounced.
This pattern — fast value for the UI, debounced value for the side effect — is the whole point. Keep them as two separate variables and the rest falls into place.
useDebounceFn — Debounce a Callback
Debouncing a value is great when the thing you want to throttle is state. But sometimes you want to debounce an action that takes arguments — an autosave, an analytics event, a resize handler — without routing it through state first. That’s useDebounceFn:
import { useDebounceFn } from ‘@reactuses/core’;
function Editor({ docId }: { docId: string }) {
const { run } = useDebounceFn((content: string) => {
saveDraft(docId, content);
}, 1000);
return (
textarea onChange={(e) => run(e.target.value)} />
);
}
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useDebounceFn(fn, wait?, options?) returns an object with three members:
const { run, cancel, flush } = useDebounceFn(fn, 1000);
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run — the debounced function. Call it as often as you like; fn only actually executes after the calls stop for wait ms. It forwards every argument through, so run(content) calls fn(content).
cancel — drop any pending invocation. Nothing fires.
flush — fire the pending invocation right now, instead of waiting out the timer.
Crucially, run always calls the latest version of your fn. Internally the hook keeps your callback in a ref, so even though the debounced wrapper is created once, it never goes stale — the docId closure problem from the setTimeout version simply doesn’t exist here. And the hook cancels any pending call automatically on unmount, so bug #1 is gone too.
useDebounce is actually built on top of useDebounceFn — it debounces a setState call and hands you the resulting value. Same engine, two ergonomics.
cancel and flush in practice
The cancel/flush pair is what raw setTimeout makes painful and a hook makes trivial. Two real cases:
function CommentBox() {
const { run: autosave, cancel, flush } = useDebounceFn(
(text: string) => saveDraft(text),
2000,
);
return (
textarea onChange={(e) => autosave(e.target.value)} />
{/* User hit “Post” — persist immediately, don’t wait out the 2s */}
button onClick={() => flush()}>Postbutton>
{/* User hit “Discard” — throw away the pending autosave */}
button onClick={() => cancel()}>Discardbutton>
>
);
}
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flush guarantees the in-flight draft is written before the post request goes out; cancel makes sure a discarded draft doesn’t get saved a beat later. Both are one call.
Value or Callback — Which One?
A quick decision rule:
Reach for useDebounce when you’re debouncing a piece of state that something else reads — a search term, a filter, a slider value feeding a chart. You want a lagging value.
Reach for useDebounceFn when you’re debouncing an action with arguments — autosave, logging, firing a network request directly. You want a lagging function, plus cancel/flush control.
If you find yourself creating a piece of state only to debounce it and then immediately fire an effect, useDebounceFn is usually the more direct tool.
Tuning: leading, trailing, and maxWait
The optional third argument is passed straight through to lodash.debounce, so you get its full options object:
useDebounce(value, 300, {
leading: false, // don’t fire on the very first call (default)
trailing: true, // fire after the pause (default)
maxWait: 1000, // …but never wait longer than 1s total
});
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Two knobs worth knowing:
leading: true fires on the first call immediately, then debounces the rest. Good for “respond instantly, then settle” interactions — the first click of a button feels snappy while rapid repeats are absorbed.
maxWait caps the total delay. With a pure trailing debounce, a user who types continuously for ten seconds gets zero updates until they stop. maxWait: 1000 forces an update at least once a second even mid-burst — the difference between a search box that feels alive and one that feels frozen.
SSR Safety
Both hooks are safe to render on the server. They touch no window, document, or browser timer during render — the debounced work only ever runs inside effects, which React never executes on the server. Drop them into a Next.js, Remix, or Astro component and there’s no typeof window guard to write, no hydration warning to chase. (If SSR-safety is a running theme in your codebase, SSR-Safe React Hooks goes deeper.)
The Rate-Limiting Family
useDebounce has three close relatives in ReactUse; pick by what you’re limiting and which shape you need:
The throttle pair mirrors the debounce pair exactly — same (value/fn, wait, options) signature, same return shapes — but enforces a steady cadence instead of waiting for silence. Use throttle for things that should update during a continuous gesture (scroll position, drag coordinates, a live progress readout); use debounce for things that should update only after it ends (search, autosave, validation). The full mental model is in Debounce vs Throttle in React: When to Use Which.
Takeaways
A hand-rolled setTimeout debounce inside a component ships three bugs by default: it leaks on unmount, it captures stale closures, and it gets copy-pasted.
useDebounce(value, wait) gives you a lagging copy of a value — type into the fast one, run effects off the slow one. Perfect for search-as-you-type.
useDebounceFn(fn, wait) debounces an action and hands you { run, cancel, flush }. run always calls your latest callback (no stale closures) and auto-cancels on unmount.
Use flush to commit a pending call early (submit) and cancel to drop it (discard).
The third argument is lodash.debounce options — leading for instant-first-call, maxWait to cap the delay so long bursts still update.
Both are SSR-safe and sit alongside useThrottle/useThrottleFn for the fixed-rate case.
Grab them from @reactuses/core and delete your clearTimeout boilerplate.
