javascript 69 lines · 10 steps

Building a swipe-to-dismiss gesture in JS

How touch events track a horizontal drag and either fling an element away or snap it back.

Explained by highlit
Intermediate touch-events gesture-detection dom-manipulation event-listeners cleanup
1const SWIPE_THRESHOLD = 80;
2const MAX_TRANSLATE = 120;
3 
4export function attachSwipeToDismiss(element, onDismiss) {
5 let startX = 0;
6 let startY = 0;
7 let currentX = 0;
8 let tracking = false;
9 let horizontal = false;
10 
11 function onTouchStart(e) {
12 const touch = e.touches[0];
13 startX = touch.clientX;
14 startY = touch.clientY;
15 currentX = 0;
16 tracking = true;
17 horizontal = false;
18 element.style.transition = '';
19 }
20 
21 function onTouchMove(e) {
22 if (!tracking) return;
23 const touch = e.touches[0];
24 const dx = touch.clientX - startX;
25 const dy = touch.clientY - startY;
26 
27 if (!horizontal) {
28 if (Math.abs(dx) < 10 && Math.abs(dy) < 10) return;
29 horizontal = Math.abs(dx) > Math.abs(dy);
30 if (!horizontal) {
31 tracking = false;
32 return;
33 }
34 }
35 
36 e.preventDefault();
37 currentX = Math.max(-MAX_TRANSLATE, Math.min(MAX_TRANSLATE, dx));
38 element.style.transform = `translateX(${currentX}px)`;
39 element.style.opacity = String(1 - Math.abs(currentX) / (MAX_TRANSLATE * 1.5));
40 }
41 
42 function onTouchEnd() {
43 if (!tracking) return;
44 tracking = false;
45 element.style.transition = 'transform 0.25s ease, opacity 0.25s ease';
46 
47 if (Math.abs(currentX) >= SWIPE_THRESHOLD) {
48 const direction = currentX > 0 ? 1 : -1;
49 element.style.transform = `translateX(${direction * window.innerWidth}px)`;
50 element.style.opacity = '0';
51 element.addEventListener('transitionend', () => onDismiss(element), { once: true });
52 } else {
53 element.style.transform = '';
54 element.style.opacity = '';
55 }
56 }
57 
58 element.addEventListener('touchstart', onTouchStart, { passive: true });
59 element.addEventListener('touchmove', onTouchMove, { passive: false });
60 element.addEventListener('touchend', onTouchEnd);
61 element.addEventListener('touchcancel', onTouchEnd);
62 
63 return () => {
64 element.removeEventListener('touchstart', onTouchStart);
65 element.removeEventListener('touchmove', onTouchMove);
66 element.removeEventListener('touchend', onTouchEnd);
67 element.removeEventListener('touchcancel', onTouchEnd);
68 };
69}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Detecting gesture direction early lets you claim horizontal swipes while leaving vertical scrolling untouched.
  2. 2Clamping the drag distance and toggling CSS transitions keeps the follow-the-finger feel separate from the snap-back animation.
  3. 3Returning a teardown function makes an event-heavy setup safe to unbind when the element goes away.

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