Detect if an element is in the viewport using a React Hook. Utilizes the Intersection Observer API, so check for compatibility.
npm install react-hook-inview
Optional: Install a polyfill for browsers that don't support
IntersectionObserver
yet (i.e. Safari 12).
The hook in its most basic form returns a ref and a boolean.
const [ref, inView] = useInView()
That's all you need to get started, but it does a lot more.
In this example, the boolean is used to toggle some text on and off when the element is fully in the viewport.
import React from 'react'
import { useInView } from 'react-hook-inview'
const Component = () => {
const [ref, isVisible] = useInView({
threshold: 1,
})
return <div ref={ref}>{isVisible ? 'Hello World!' : ''}</div>
}
The hook returns a tuple with four items:
- A
ref
callback, used to set observer on an element. - A
boolean
when the element is in the viewport. - The
IntersectionObserverEntry
- The
IntersectionObserver
itself
const [ref, inView, entry, observer] = useInView(options, [...state])
These are the default options.
{
root?: RefObject<Element> | null, // Optional, must be a parent of your ref
rootMargin?: string, // '0px' or '0px 0px 0px 0px', also accepts '%' unit
threshold?: number | number[], // 0.5 or [0, 0.5, 1]
unobserveOnEnter?: boolean, // Set 'true' to run only once
onEnter?: (entry?, observer?) => void, // See below
onLeave?: (entry?, observer?) => void, // See below
target?: RefObject<Element> | null, // *DEPRECATED* Supply your own ref object
defaultInView?: boolean, // false
}
NOTE If you're updating from < version 4.0.0.
, you might have noticed an
API changed. The target
option has been deprecated, but still works the same
way.
onEnter
and onLeave
recieve a callback function that returns an
IntersectionObserverEntry
and the IntersectionObserver
itself. The two
arguments are entirely optional.
function onEnter(entry, observer) {
// entry.boundingClientRect
// entry.intersectionRatio
// entry.intersectionRect
// entry.isIntersecting
// entry.rootBounds
// entry.target
// entry.time
}
NOTE: If you supply an array with multiple values to threshold
, onEnter
will be called each time the element intersects with the top and bottom of
the viewport. onLeave
will on trigger once the element has left the viewport
at the first threshold specified.
For performance reasons, the hook is only triggered once on mount. However,
this means you can't access updated state in the onEnter/onLeave
callbacks.
An optional second argument will retrigger the hook to mitigate this.
// Some other state
const [state, setState] = useState(false)
const [ref, inView] = useInView(
{
onEnter: () => console.log(state),
},
[state], // <- Will update callback
)
This will remount the intersection observer, and may have unintended side effects. Use this feature with caution.
An alternate hook that allows you to just supply the intersection observer callback. This approach is gives you a little more flexibilty than using the callbacks in the original hook as it doesn't obfuscate the Intersection Observer API as much.
const ref = useInViewEffect(callback, options, [...state])
import React, { useState } from 'react'
import { useInViewEffect } from 'react-hook-inview'
const Component = () => {
const [isVisible, setIsVisible] = useState(false)
const ref = useInViewEffect(
([entry], observer) => {
if (entry.isIntersecting) {
observer.unobserve(entry.target)
}
setIsVisible(entry.isIntersecting)
},
{ threshold: 0.5 },
)
return <div ref={ref}>{isVisible ? 'Hello World!' : ''}</div>
}
Keep in mind that the first argument will return an array.
The useInViewEffect
hook has more limited options that mirror the default
API.
{
root?: RefObject<Element> | null, // Optional, must be a parent of your ref
rootMargin?: string, // '0px' or '0px 0px 0px 0px', also accepts '%' unit
threshold?: number | number[], // 0.5 or [0, 0.5, 1]
}