How to add class in element on scroll React js - reactjs

Question

How to add class in element on scroll React js, I want to add class in on scroll and remove that class if on top of the page.
import React from "react"
import { Link } from "react-router"
import { prefixLink } from "gatsby-helpers"
import Helmet from "react-helmet"
import { config } from "config"
module.exports = React.createClass({
propTypes() {
return {
children: React.PropTypes.any,
}
},
render() {
window.addEventListener('scroll', (event) => {
});
return (
<div>
<header className="header">
<div className="top-bar">
<span>678-827-2782 </span>
<span> hellohello#knotel.com</span>
<button>Login</button>
</div>
</header>
{this.props.children}
</div>
)
},
})

Answer 1

If you want to use React Hooks in 2020 stateless component
const [scroll, setScroll] = useState(false);
useEffect(() => {
window.addEventListener("scroll", () => {
setScroll(window.scrollY > 50);
});
}, []);
and use it anywhere in your code
className={scroll ? "bg-black" : "bg-white"}
setScroll(window.scrollY > 50); here 50 specify the height.

Answer 2

Use state to manage classnames and update state in the scroll event. Also, you should move the scroll event binding into the componentDidMount function instead of render.
import React from "react"
import { Link } from "react-router"
import { prefixLink } from "gatsby-helpers"
import Helmet from "react-helmet"
import { config } from "config"
module.exports = React.createClass({
propTypes() {
return {
children: React.PropTypes.any,
}
},
componentDidMount(){
window.addEventListener('scroll', () => {
let activeClass = 'normal';
if(window.scrollY === 0){
activeClass = 'top';
}
this.setState({ activeClass });
});
}
render() {
return (
<div>
<header className="header">
<div className={`top-bar ${this.state.activeClass}`}>
<span>678-827-2782 </span>
<span> hellohello#knotel.com</span>
<button>Login</button>
</div>
</header>
{this.props.children}
</div>
)
},
})

Answer 3

import React, { useState, useEffect } from "react"
import { Link } from "react-router"
import { prefixLink } from "gatsby-helpers"
import Helmet from "react-helmet"
import { config } from "config"
export default function Header(props) {
const [scroll, setScroll] = useState(false)
useEffect(() => {
window.addEventListener("scroll", () => {
setScroll(window.scrollY > 10)
})
}, [])
return (
<header className={scroll ? "main-header scrolled" : "main-header"}>
</header>
)
}

Answer 4

One more variant with hooks and cleanup to avoid memory leaks, if the browser is not handled it properly.
const [isScrollValueMoreThanHeaderHeight, setIsScrollValueMoreThanHeaderHeight] = useState(false);
//here 96(px) - height of current header
useEffect(() => {
const handleScroll = () => {
setIsScrollValueMoreThanHeaderHeight(window.scrollY > 96);
}
window.addEventListener('scroll', handleScroll)
return () => window.removeEventListener('scroll', handleScroll);
},[])
And then used it in a ternary way to change class
className={isScrollValueMoreThanHeaderHeight ? "class1" : "class2"}