How can I apply a global scroll event to multiple React components? - reactjs

Question

I'm building a React app and I'd like to have a global CSS class that is used to fade in components when they appear in the viewport.
jQuery
With jQuery, I might do something like this:
const windowHeight = (window.innerHeight || document.documentElement.clientHeight);
const windowWidth = (window.innerWidth || document.documentElement.clientWidth);
isInViewport(el) {
const rect = el.getBoundingClientRect();
const vertInView = (rect.top <= windowHeight) && ((rect.top + rect.height) >= 0);
const horInView = (rect.left <= windowWidth) && ((rect.left + rect.width) >= 0);
return (vertInView && horInView);
};
$(window).scroll(function(e) {
$('.animate').each(function() {
if(isInViewport($(this)[0])) {
$(this).addClass('animate--active');
}
});
});
On scroll, I'd check each element with the animate class and if that element is in the viewport, add the animate--active class to it, which will fade it in.
React
In React, I've moved my isInViewport() function to a global Helpers.js file so any component can make use of it, but I've had to add the scroll event and the dynamic class to every component, which makes for a lot of duplicated code. For example:
import { isInViewport } from './Helpers.js';
function MyComponent(props) {
const [inViewport, setInViewport] = useState(false);
const myComponentRef = useRef();
function handleScroll(e) {
setInViewport(isInViewport(myComponentRef.current));
}
useEffect(() => {
window.addEventListener('scroll', handleScroll);
// unmount
return () => {
window.removeEventListener('scroll', handleScroll);
};
}, []);
const classes = (inViewport) ? 'animate animate--active' : 'animate';
return (
<section className={classes} ref={myComponentRef}>
</section>
);
}
As far as I can tell, this would be the React way of doing this, and this does work, but again, it means that every component would require its own state variable, scroll event and class declaration, which adds up to a lot of repetition. Is there a better way of doing this?

Answer 1

Custom Hooks, Custom Hooks, Custom Hooks
import { isInViewport } from './Helpers.js';
function useIsInViewPort(ref) {
const [inViewport, setInViewport] = React.useState(false);
function handleScroll(e) {
setInViewport(isInViewport(ref.current));
}
React.useEffect(() => {
window.addEventListener('scroll', handleScroll);
// unmount
return () => {
window.removeEventListener('scroll', handleScroll);
};
}, []);
return inViewport;
}
function Acmp(props) {
const ref = React.useRef();
const inViewport = useIsInViewPort(ref);
const classes = (inViewport) ? 'animate animate--active' : 'animate';
return (
<section className={classes} ref={ref}>
</section>
);
}
function Bcmp(props) {
const ref = React.useRef();
const inViewport = useIsInViewPort(ref);
return (
<section className={classes} ref={ref}>
</section>
);
}