CSS Scroll Snap Points with navigation (next, previous) buttons
I've just done something similar recently. The idea is to use IntersectionObserver to keep track of which item is in view currently and then hook up the previous/next buttons to event handler calling Element.scrollIntoView().
Anyway, Safari does not currently support scroll behavior options. So you might want to polyfill it on demand with polyfill.app service.
let activeIndex = 0;
const container = document.querySelector("#container");
const elements = [...document.querySelectorAll("#container div")];
function handleIntersect(entries){
const entry = entries.find(e => e.isIntersecting);
if (entry) {
const index = elements.findIndex(
e => e === entry.target
);
activeIndex = index;
}
}
const observer = new IntersectionObserver(handleIntersect, {
root: container,
rootMargin: "0px",
threshold: 0.75
});
elements.forEach(el => {
observer.observe(el);
});
function goPrevious() {
if(activeIndex > 0) {
elements[activeIndex - 1].scrollIntoView({
behavior: 'smooth'
})
}
}
function goNext() {
if(activeIndex < elements.length - 1) {
elements[activeIndex + 1].scrollIntoView({
behavior: 'smooth'
})
}
}#container {
scroll-snap-type: y mandatory;
overflow-y: scroll;
border: 2px solid var(--gs0);
border-radius: 8px;
height: 60vh;
}
#container div {
scroll-snap-align: start;
display: flex;
justify-content: center;
align-items: center;
font-size: 4rem;
}
#container div:nth-child(1) {
background: hotpink;
color: white;
height: 50vh;
}
#container div:nth-child(2) {
background: azure;
height: 40vh;
}
#container div:nth-child(3) {
background: blanchedalmond;
height: 60vh;
}
#container div:nth-child(4) {
background: lightcoral;
color: white;
height: 40vh;
}<div id="container">
<div>1</div>
<div>2</div>
<div>3</div>
<div>4</div>
</div>
<button onClick="goPrevious()">previous</button>
<button onClick="goNext()">next</button>Nice question! I took this as a challenge.
So, I increased JavaScript for it to work dynamically. Follow my detailed solution (in the end the complete code):
First, add position: relative to the .container, because it need to be reference for scroll and height checkings inside .container.
Then, let's create 3 global auxiliary variables:
1) One to get items scroll positions (top and bottom) as arrays into an array. Example: [[0, 125], [125, 280], [280, 360]] (3 items in this case).
3) One that stores half of .container height (it will be useful later).
2) Another one to store the item index for scroll position
var carouselPositions;
var halfContainer;
var currentItem;
Now, a function called getCarouselPositions that creates the array with items positions (stored in carouselPositions) and calculates the half of .container (stored in halfContainer):
function getCarouselPositions() {
carouselPositions = [];
document.querySelectorAll('#container div').forEach(function(div) {
carouselPositions.push([div.offsetTop, div.offsetTop + div.offsetHeight]); // add to array the positions information
})
halfContainer = document.querySelector('#container').offsetHeight/2;
}
getCarouselPositions(); // call it once
Let's replace the functions on buttons. Now, when you click on them, the same function will be called, but with "next" or "previous" argument:
<button onClick="goCarousel('previous')">previous</button>
<button onClick="goCarousel('next')">next</button>
Here is about the goCarousel function itself:
First, it creates 2 variables that store top scroll position and bottom scroll position of carousel.
Then, there are 2 conditionals to see if the current carousel position is on most top or most bottom.
If it's on top and clicked "next" button, it will go to the second item position. If it's on bottom and clicked "previous" button, it will go the previous one before the last item.
If both conditionals failed, it means the current item is not the first or the last one. So, it checks to see what is the current position, calculating using the half of the container in a loop with the array of positions to see what item is showing. Then, it combines with "previous" or "next" checking to set the correct next position for currentItem variable.
Finally, it goes to the correct position through scrollTo using currentItem new value.
Below, the complete code:
var carouselPositions;
var halfContainer;
var currentItem;
function getCarouselPositions() {
carouselPositions = [];
document.querySelectorAll('#container div').forEach(function(div) {
carouselPositions.push([div.offsetTop, div.offsetTop + div.offsetHeight]); // add to array the positions information
})
halfContainer = document.querySelector('#container').offsetHeight/2;
}
getCarouselPositions(); // call it once
function goCarousel(direction) {
var currentScrollTop = document.querySelector('#container').scrollTop;
var currentScrollBottom = currentScrollTop + document.querySelector('#container').offsetHeight;
if (currentScrollTop === 0 && direction === 'next') {
currentItem = 1;
} else if (currentScrollBottom === document.querySelector('#container').scrollHeight && direction === 'previous') {
console.log('here')
currentItem = carouselPositions.length - 2;
} else {
var currentMiddlePosition = currentScrollTop + halfContainer;
for (var i = 0; i < carouselPositions.length; i++) {
if (currentMiddlePosition > carouselPositions[i][0] && currentMiddlePosition < carouselPositions[i][1]) {
currentItem = i;
if (direction === 'next') {
currentItem++;
} else if (direction === 'previous') {
currentItem--
}
}
}
}
document.getElementById('container').scrollTo({
top: carouselPositions[currentItem][0],
behavior: 'smooth'
});
}
window.addEventListener('resize', getCarouselPositions);#container {
scroll-snap-type: y mandatory;
overflow-y: scroll;
border: 2px solid var(--gs0);
border-radius: 8px;
height: 60vh;
position: relative;
}
#container div {
scroll-snap-align: start;
display: flex;
justify-content: center;
align-items: center;
font-size: 4rem;
}
#container div:nth-child(1) {
background: hotpink;
color: white;
height: 50vh;
}
#container div:nth-child(2) {
background: azure;
height: 40vh;
}
#container div:nth-child(3) {
background: blanchedalmond;
height: 60vh;
}
#container div:nth-child(4) {
background: lightcoral;
color: white;
height: 40vh;
}<div id="container">
<div>1</div>
<div>2</div>
<div>3</div>
<div>4</div>
</div>
<button onClick="goCarousel('previous')">previous</button>
<button onClick="goCarousel('next')">next</button>Another good detail to add is to call getCarouselPositions function again if the window resizes:
window.addEventListener('resize', getCarouselPositions);
That's it.
That was cool to do. I hope it can help somehow.