To add scroll event listeners in a React component, we can set the onScroll prop of an element to an event handler function. We create the onScroll function that logs the scroll event object. Then we assign the onScroll function as the value of the onScroll prop of the div.
You should bind the listener in componentDidMount
, that way it's only created once. You should be able to store the style in state, the listener was probably the cause of performance issues.
Something like this:
componentDidMount: function() {
window.addEventListener('scroll', this.handleScroll);
},
componentWillUnmount: function() {
window.removeEventListener('scroll', this.handleScroll);
},
handleScroll: function(event) {
let scrollTop = event.srcElement.body.scrollTop,
itemTranslate = Math.min(0, scrollTop/3 - 60);
this.setState({
transform: itemTranslate
});
},
with hooks
import React, { useEffect, useState } from 'react';
function MyApp () {
const [offset, setOffset] = useState(0);
useEffect(() => {
window.onscroll = () => {
setOffset(window.pageYOffset)
}
}, []);
console.log(offset);
};
You can pass a function to the onScroll
event on the React element: https://facebook.github.io/react/docs/events.html#ui-events
<ScrollableComponent
onScroll={this.handleScroll}
/>
Another answer that is similar: https://stackoverflow.com/a/36207913/1255973
My solution for making a responsive navbar ( position: 'relative' when not scrolling and fixed when scrolling and not at the top of the page)
componentDidMount() {
window.addEventListener('scroll', this.handleScroll);
}
componentWillUnmount() {
window.removeEventListener('scroll', this.handleScroll);
}
handleScroll(event) {
if (window.scrollY === 0 && this.state.scrolling === true) {
this.setState({scrolling: false});
}
else if (window.scrollY !== 0 && this.state.scrolling !== true) {
this.setState({scrolling: true});
}
}
<Navbar
style={{color: '#06DCD6', borderWidth: 0, position: this.state.scrolling ? 'fixed' : 'relative', top: 0, width: '100vw', zIndex: 1}}
>
No performance issues for me.
to help out anyone here who noticed the laggy behavior / performance issues when using Austins answer, and wants an example using the refs mentioned in the comments, here is an example I was using for toggling a class for a scroll up / down icon:
In the render method:
<i ref={(ref) => this.scrollIcon = ref} className="fa fa-2x fa-chevron-down"></i>
In the handler method:
if (this.scrollIcon !== null) {
if(($(document).scrollTop() + $(window).height() / 2) > ($('body').height() / 2)){
$(this.scrollIcon).attr('class', 'fa fa-2x fa-chevron-up');
}else{
$(this.scrollIcon).attr('class', 'fa fa-2x fa-chevron-down');
}
}
And add / remove your handlers the same way as Austin mentioned:
componentDidMount(){
window.addEventListener('scroll', this.handleScroll);
},
componentWillUnmount(){
window.removeEventListener('scroll', this.handleScroll);
},
docs on the refs.
I found that I can't successfully add the event listener unless I pass true like so:
componentDidMount = () => {
window.addEventListener('scroll', this.handleScroll, true);
},
An example using classNames, React hooks useEffect, useState and styled-jsx:
import classNames from 'classnames'
import { useEffect, useState } from 'react'
const Header = _ => {
const [ scrolled, setScrolled ] = useState()
const classes = classNames('header', {
scrolled: scrolled,
})
useEffect(_ => {
const handleScroll = _ => {
if (window.pageYOffset > 1) {
setScrolled(true)
} else {
setScrolled(false)
}
}
window.addEventListener('scroll', handleScroll)
return _ => {
window.removeEventListener('scroll', handleScroll)
}
}, [])
return (
<header className={classes}>
<h1>Your website</h1>
<style jsx>{`
.header {
transition: background-color .2s;
}
.header.scrolled {
background-color: rgba(0, 0, 0, .1);
}
`}</style>
</header>
)
}
export default Header
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