Debouncing and throttling are techniques to control function execution frequency during high-frequency events. 1) Debouncing runs a function only after a specified delay since the last call, ideal for final state actions like search inputs. 2) Throttling runs a function at most once per specified interval, suitable for continuous feedback like scroll or mousemove events. 3) Use debounce when you need to act after a pause in events; use throttle when consistent updates are needed during prolonged activity. Both improve performance by reducing unnecessary function calls, with debouncing preventing premature execution and throttling enforcing a steady execution rate.
When dealing with high-frequency events in JavaScript—like scrolling, resizing, or typing—naive event handling can quickly tank performance. Two essential techniques to manage this are debouncing and throttling. They both limit how often a function runs, but they work differently and suit different scenarios.
Let’s break them down in plain terms, with practical examples.
What is Debouncing?
Debouncing ensures a function runs only after a certain amount of time has passed since the last time it was called. It’s like saying: “Wait until the user stops doing something before I respond.”
Common Use Case:
- Search input that triggers an API call as the user types.
If you fire an API request on every keystroke, you’ll spam the server. With debouncing, you wait until the user pauses typing (e.g., 300ms), then make the request.
Example:
function debounce(func, delay) {
let timeoutId;
return function (...args) {
clearTimeout(timeoutId);
timeoutId = setTimeout(() => func.apply(this, args), delay);
};
}
// Usage
const searchInput = document.getElementById('search');
searchInput.addEventListener('input', debounce(function(e) {
console.log('Searching for:', e.target.value);
}, 300));Here’s what happens:
- User types: "hello"
- Each keystroke resets the timer.
- Only after 300ms of inactivity does the final function run.
? Think of it like a shower: you don’t want to turn on the water every time someone taps the knob. You wait until they’ve stopped fiddling and then adjust.
What is Throttling?
Throttling ensures a function runs at most once per specified time interval, no matter how often it's triggered. It’s like saying: “I’ll respond, but only every X milliseconds.”
Common Use Case:
- Handling scroll or mousemove events where you want consistent updates without overwhelming the browser.
Example:
function throttle(func, limit) {
let inThrottle;
return function (...args) {
if (!inThrottle) {
func.apply(this, args);
inThrottle = true;
setTimeout(() => inThrottle = false, limit);
}
};
}
// Usage
window.addEventListener('scroll', throttle(() => {
console.log('Scroll position:', window.scrollY);
}, 100)); // Logs at most every 100msSo even if the user scrolls rapidly, the callback runs only once every 100ms.
? Think of it like a water faucet with a flow restrictor—you can turn it on full blast, but water only comes out at a steady rate.
Key Differences
| Feature | Debouncing | Throttling |
|---|---|---|
| When it runs | After a pause in events | At regular intervals |
| Best for | Final state actions (e.g., search) | Continuous feedback (e.g., scroll) |
| Frequency | Once after delay | Once per interval |
| Response style | Wait-and-respond | Steady pulse |
When to Use Which?
-
? Use debounce when:
- You care about the final state after a burst of events.
- Examples: search input, form validation, window resize (adjusting layout once).
-
? Use throttle when:
- You need regular updates during an ongoing event.
- Examples: scroll tracking, mouse movement, animation progress.
Bonus: Real-World Gotchas
- Memory leaks: Always clean up event listeners if components unmount (e.g., in React useEffect cleanup).
-
thiscontext: Use.apply(this, args)or arrow functions to preserve context. -
Leading vs trailing edge:
- Some advanced debounce/throttle implementations let you choose whether the function runs at the start (leading) or end (trailing) of the delay.
- Example: A button that should respond immediately but not again for 1 second → use leading-edge throttle.
Basically, debouncing waits for peace before acting; throttling sets a maximum pace. Both are simple to implement and vital for smooth, performant apps. Pick the right one based on whether you need a final result or steady updates.
The above is the detailed content of JavaScript Performance: Debouncing and Throttling Explained. For more information, please follow other related articles on the PHP Chinese website!
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