Created
February 23, 2018 06:45
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How to get Y scroll position in React
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import React, { Component } from 'react' | |
import UserDetails from './UserDetails' | |
/** | |
* This utility function allows function calls to be debounced. | |
* @param {Function} func Function that requires debouncing | |
* @param {Number} wait Wait time in milliseconds between successive invocations | |
*/ | |
const debounce = (func, wait) => { | |
let timeout | |
return (...args) => { | |
clearTimeout(timeout) | |
timeout = setTimeout(() => func.apply(this, args), wait) | |
} | |
} | |
class NavContainer extends Component { | |
constructor(props) { | |
super(props) | |
this.state = { | |
scrollPositionY: 0, | |
} | |
} | |
componentDidMount() { | |
// 32 is the number of milliseconds to debounce | |
// I picked this because it's approx 2 frames (ie: 16.7 * 2) | |
return window.addEventListener('scroll', debounce(this.handleScroll, 32)) | |
} | |
componentWillUnmount() { | |
return window.removeEventListener('scroll', debounce(this.handleScroll, 32)) | |
} | |
handleScroll = () => { | |
// + is unary operator, same as Number(scrollPositionY) | |
const scrollPositionY = +window.scrollY | |
return this.setState({ scrollPositionY }) | |
} | |
render() { | |
// !! coerces value to be a Boolean | |
// we want it to be true or false (true if scrollPositionY > 0) | |
// it works because scrollPositionY === 0 is falsy | |
const isScrolling = !!this.state.scrollPositionY | |
return ( | |
<div className={(isScrolling) ? 'nav isScrolling' : 'nav'}> | |
<UserDetails isScrolling={isScrolling} /> | |
</div> | |
) | |
} | |
} |
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Thanks for this concise implementation.
Mind that this implementation may trigger too much rendering.