react-cool-inview is a React hook / component API that monitors an element enters or leaves the viewport (or another element) with performant and efficient way, using Intersection Observer. It's lightweight and super flexible, which can cover all the cases that you need, like lazy-loading images and videos, infinite scroll web app, triggering animations, tracking impressions, and more. Try it you will ❤️ it!
⚡️ Try yourself: https://react-cool-inview.netlify.app
Features
- 🚀 Monitors elements with performant and non-main-thread blocking way, using Intersection Observer.
- 🎣 Easy to use, based on React hook / component.
- 🎛 Super flexible API design which can cover all the cases that you need.
- 🖱️ Supports scroll direction, cool right?
- ✌🏻 Supports Intersection Observer v2. (https://github.com/wellyshen/react-cool-inview#use-your-own-ref).
- 📜 Supports TypeScript type definition.
- 🗄️ Server-side rendering compatibility.
- 🦔 Tiny size (~ 1.2kB gzipped). No external dependencies, aside for the
react
.
Usage
react-cool-inview
has a flexible API design, it can cover simple to complex use cases for you. Here are some ideas for how you can use it.
Basic Use Case
To monitor an element enters or leaves the viewport by the inView
state and useful sugar events.
import { useInView } from "react-cool-inview";
const App = () => {
const { observe, unobserve, inView, scrollDirection, entry } = useInView({
threshold: 0.25, // Default is 0
onChange: ({ inView, scrollDirection, entry, observe, unobserve }) => {
// Triggered whenever the target meets a threshold, e.g. [0.25, 0.5, ...]
unobserve(); // To stop observing the current target element
observe(); // To re-start observing the current target element
},
onEnter: ({ scrollDirection, entry, observe, unobserve }) => {
// Triggered when the target enters the viewport
},
onLeave: ({ scrollDirection, entry, observe, unobserve }) => {
// Triggered when the target leaves the viewport
},
// More useful options...
});
return <div ref={observe}>{inView ? "Hello, I am 🤗" : "Bye, I am 😴"}</div>;
};
Using as a Component
Changes HelloText
when it enters the viewport. The options can be passed through the props.
import { InView } from "react-cool-inview";
const HelloText = ({ inView, observe }) => (
<div ref={observe}>{inView ? "Hello, I am 🤗" : "Bye, I am 😴"}</div>
);
const App = () => (
<InView unobserveOnEnter>
<HelloText />
</InView>
);
💡
InView
passesobserve
and other props to theHelloText
.
Lazy loading Images
It's super easy to build an image lazy-loading component with react-cool-inview
to boost the performance of your web app.
import { useInView } from "react-cool-inview";
const LazyImage = ({ width, height, ...rest }) => {
const { observe, inView } = useInView({
// Stop observe when the target enters the viewport, so the "inView" only triggered once
unobserveOnEnter: true,
// For better UX, we can grow the root margin so the image will be loaded before it comes to the viewport
rootMargin: "50px",
});
return (
<div className="placeholder" style={{ width, height }} ref={observe}>
{inView && <img {...rest} />}
</div>
);
};
Infinite Scroll
Infinite scroll is a popular design technique like Facebook and Twitter feed etc., new content being loaded as you scroll down a page. The basic concept as below.
import { useState } from "react";
import { useInView } from "react-cool-inview";
import axios from "axios";
const App = () => {
const [todos, setTodos] = useState(["todo-1", "todo-2", "..."]);
const { observe } = useInView({
// For better UX, we can grow the root margin so the data will be loaded earlier
rootMargin: "50px 0px",
// When the last item comes to the viewport
onEnter: ({ unobserve, observe }) => {
// Pause observe when loading data
unobserve();
// Load more data
axios.get("/todos").then((res) => {
setTodos([...todos, ...res.todos]);
// Resume observe after loading data
observe();
});
},
});
return (
<div>
{todos.map((todo, idx) => (
<div ref={idx === todos.length - 1 ? observe : null}>{todo}</div>
))}
</div>
);
};
Trigger Animations
Another great use case is to trigger CSS animations once they are visible to the users.
import { useInView } from "react-cool-inview";
const App = () => {
const { observe, inView } = useInView({
// Stop observe when the target enters the viewport, so the "inView" only triggered once
unobserveOnEnter: true,
// Shrink the root margin, so the animation will be triggered once the target reach a fixed amount of visible
rootMargin: "-100px 0px",
});
return (
<div className="container" ref={observe}>
<div className={inView ? "fade-in" : ""}>I'm a 🍟</div>
</div>
);
};
Track Impressions
react-cool-inview
can also play as an impression tracker, helps you fire an analytic event when a user sees an element or advertisement.
import { useInView } from "react-cool-inview";
const App = () => {
const { observe } = useInView({
// For an element to be considered "seen", we'll say it must be 100% in the viewport
threshold: 1,
onEnter: ({ unobserve }) => {
// Stop observe when the target enters the viewport, so the callback only triggered once
unobserve();
// Fire an analytic event to your tracking service
someTrackingService.send("🍋 is seen");
},
});
return <div ref={observe}>I'm a 🍋</div>;
};
Scrolling Direction
react-cool-inview
not only monitors an element enters or leaves the viewport but also tells you its scroll direction by the scrollDirection
object. The object contains vertical (y-axios) and horizontal (x-axios) properties, they're calculated whenever the target element meets a threshold
. If there's no enough condition for calculating, the value of the properties will be undefined
. In addition, the value of the properties will sync with the scrolling direction of the viewport.
import { useInView } from "react-cool-inview";
const App = () => {
const {
observe,
inView,
// vertical will be "up" or "down", horizontal will be "left" or "right"
scrollDirection: { vertical, horizontal },
} = useInView({
// Scroll direction is calculated whenever the target meets a threshold
// more trigger points the calculation will be more instant and accurate
threshold: [0.2, 0.4, 0.6, 0.8, 1],
onChange: ({ scrollDirection }) => {
// We can also access the scroll direction from the event object
console.log("Scroll direction: ", scrollDirection.vertical);
},
});
return (
<div ref={observe}>
<div>{inView ? "Hello, I am 🤗" : "Bye, I am 😴"}</div>
<div>{`You're scrolling ${vertical === "up" ? "⬆️" : "⬇️"}`}</div>
</div>
);
};
Intersection Observer v2
The Intersection Observer v1 can perfectly tell you when an element is scrolled into the viewport, but it doesn't tell you whether the element is covered by something else on the page or whether the element has any visual effects applied to it (like transform
, opacity
, filter
etc.) that can make it invisible. The main concern that has surfaced is how this kind of knowledge could be helpful in preventing clickjacking and UI redress attacks (read this article to learn more).
If you want to track the click-through rate (CTR) or impression of an element, which is actually visible to a user, Intersection Observer v2 can be the savior. Which introduces a new boolean field named isVisible. A true
value guarantees that an element is visible on the page and has no visual effects applied on it. A false
value is just the opposite. The characteristic of the isVisible
is integrated with the inView
state and related events (like onEnter, onLeave etc.) to provide a better DX for you.
When using the v2, there're somethings we need to know:
- Check browser compatibility. If a browser doesn't support the v2, we will fallback to the v1 behavior.
- Understand how visibility is calculated.
- Visibility is much more expensive to compute than intersection, only use it when needed.
To use Intersection Observer v2, we must set the trackVisibility
and delay
options.
import { useInView } from "react-cool-inview";
const App = () => {
// With Intersection Observer v2, the "inView" not only tells you the target
// is intersecting with the root, but also guarantees it's visible on the page
const { observe, inView } = useInView({
// Track the actual visibility of the target
trackVisibility: true,
// Set a minimum delay between notifications, it must be set to 100 (ms) or greater
// For performance perspective, use the largest tolerable value as much as possible
delay: 100,
onEnter: () => {
// Triggered when the target is visible and enters the viewport
},
onLeave: () => {
// Triggered when the target is visible and leaves the viewport
},
});
return <div ref={observe}>{inView ? "Hello, I am 🤗" : "Bye, I am 😴"}</div>;
};
Thanks for reading, for more usage details check out the project's GitHub page: https://github.com/wellyshen/react-cool-inview
You can also install this package is distributed via npm.
$ yarn add react-cool-inview
# or
$ npm install --save react-cool-inview
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