Debounce vs Throttle — hand-rolled
Build tiny debounce and throttle utilities. Practice trailing and leading variants and know when to pick each.
Debounce vs Throttle — hand-rolled is a free JavaScript Academy lesson on CoddyKit — lesson 2 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the JavaScript Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Overview
Goal: Control noisy events.
- Debounce: wait for quiet, then run once
- Throttle: run at most once per interval
- Leading vs trailing calls
- Tiny, readable helpers
Debounce (trailing)
Trailing debounce resets a timer on each event and runs once when things calm down.
// Debounce (trailing): run once after events stop
function debounce(fn, wait) {
let t = null;
return function (...args) {
clearTimeout(t);
t = setTimeout(function () {
fn.apply(null, args);
}, wait);
};
}
// Simulate rapid events: only the last triggers the call
const debouncedLog = debounce(function (msg) {
console.log("debounced:", msg);
}, 10);
for (let i = 0; i < 5; i++) {
setTimeout(function () {
debouncedLog("final after bursts");
}, i * 3);
}
Debounce (leading)
Leading debounce fires immediately, then blocks repeats until the quiet window ends.
// Debounce (leading): first call fires immediately, then ignore until quiet
function debounceLeading(fn, wait) {
let t = null;
return function (...args) {
if (t === null) {
fn.apply(null, args);
}
clearTimeout(t);
t = setTimeout(function () {
t = null;
}, wait);
};
}
// Demo: first call prints quickly; later bursts are ignored until quiet
const firstTap = debounceLeading(function (x) {
console.log("leading:", x);
}, 12);
for (let i = 0; i < 4; i++) {
setTimeout(function () {
firstTap("first-then-wait");
}, i * 3);
}
Throttle (leading)
Throttle limits calls to one per time window, dropping extras.
// Throttle (leading): at most once per interval
function throttle(fn, wait) {
let last = 0;
return function (...args) {
const now = Date.now();
if (now - last >= wait) {
last = now;
fn.apply(null, args);
}
};
}
// Demo: many events, but prints at most once every 10ms
const throttled = throttle(function (n) {
console.log("throttled:", n);
}, 10);
for (let i = 0; i < 10; i++) {
setTimeout(function () {
throttled(i);
}, i * 2);
}
Throttle (trailing)
Trailing throttle ensures you still get the latest value at the end of the window.
// Throttle (trailing): schedule the last call within the window
function throttleTrailing(fn, wait) {
let last = 0;
let timer = null;
let queuedArgs = null;
function invoke(args) {
last = Date.now();
fn.apply(null, args);
}
return function (...args) {
const now = Date.now();
const remaining = wait - (now - last);
if (remaining <= 0) {
// Window passed: run now
clearTimeout(timer);
timer = null;
queuedArgs = null;
invoke(args);
} else {
// Queue the latest args to run at the end of the window
queuedArgs = args;
clearTimeout(timer);
timer = setTimeout(function () {
timer = null;
if (queuedArgs) {
invoke(queuedArgs);
queuedArgs = null;
}
}, remaining);
}
};
}
// Demo: last value in a burst is printed after the window
const trail = throttleTrailing(function (x) {
console.log("trail:", x);
}, 10);
for (let i = 0; i < 6; i++) {
setTimeout(function () {
trail("v" + i);
}, i * 3);
}
When to use which?
Choosing:
- Debounce: search-as-you-type, resize — run after user stops.
- Throttle: scroll/drag — limit calls to steady pace.
- Leading for instant feedback; trailing to capture final value.
Debounce vs throttle quiz
Quick check: Limit calls per window.
Recap
Recap: You wrote trailing and leading debounce, a simple leading throttle, and a light trailing throttle. Pick debounce for “after user stops”, throttle for “steady pace”.
Frequently asked questions
Is the “Debounce vs Throttle — hand-rolled” lesson free?
Yes — the full text of “Debounce vs Throttle — hand-rolled” is free to read here on the web, and the JavaScript Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the JavaScript Academy course, upgrade to CoddyKit PRO.
What will I learn in “Debounce vs Throttle — hand-rolled”?
Build tiny debounce and throttle utilities. Practice trailing and leading variants and know when to pick each. You practise JavaScript Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start JavaScript Academy?
No prior experience is required. JavaScript Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “Debounce vs Throttle — hand-rolled” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this JavaScript Academy lesson?
Yes. Every JavaScript Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- setTimeout, setInterval, and timer drift
- Debounce vs Throttle — hand-rolled
- Animation Timing — intro with time-based loops