React Lazy Loading - It is easy to integrate with React to Lazyload components, Images, etc. It will monitor element and tell you when element enters into the viewport. So that can perform any operation when the component in viewport and initial load will get reduce. Implementing "infinite scrolling" web sites, where more and more content is loaded and rendered as you scroll, so that the user doesn't have to flip through pages.
Internally used Intersection Observer API

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• 🎧 Hooks or Component - With useVisibilityHook it's easier to monitor elements and perform any operations.
• 🔥 Performance - No multiple listener for scroll, resize, etc.
• 🔦 Bundle - Light weight, ~3.5kb
• 🎁 Features - forceVisible, forceCheck to manually perform operations.
• 💥 Memory optimization - Observer will disconnect once component reached viewport/unmount

React Lazy Load requires React v16.8 or later.

npm install --save react-observer-api

isVisible will be true once DOM is visible in the viewport.
setElement need to pass it to the ref as shown below.

import { useVisibilityHook } from 'react-observer-api';

export default () => {
    const { setElement, isVisible } = useVisibilityHook();

    useEffect(() => {
        if (isVisible) {
            ...Logics/API call can trigger by watching isVisible property
        }
    }, [isVisible])

    return {
        <div ref={setElement}>
            {isVisible && (
                <>
                    ...Component need to render goes here....
                <>
            )}
        </div>
    }
}

It allow to pass config options as param (optional).

{
    root: null,
    rootMargin: '0px',
    threshold: 1.0,
    always: false
}

For more details about options and usage, Click here

import { useVisibilityHook } from 'react-observer-api';

export default () => {
    const { setElement, isVisible } = useVisibilityHook({
        threshold: 0.5,
        rootMargin: '100px',
        always: false
    });
    ...
}

For some cases, you may want to continue to observe the dom node as it enters and exits the viewport. In this scenario, passing always: true in the config will enable this.

useVisibilityHook({ always: true });

<LazyLoad config={{ always: true }}>

For some case, based on condition/logic may need to show the dom before it reaches to viewport. In that scenario, by calling forceVisible() will load the dom.

import { useVisibilityHook } from 'react-observer-api';

export default () => {
    const { setElement, isVisible, forceVisible } = useVisibilityHook();

    useEffect(() => {
        forceVisible(); // isVisible become true, by manually calling this method.
    }, [])
    
    return {
        <div ref={setElement}>
            {isVisible && (
                <>
                    ...Component need to render goes here....
                <>
            )}
        </div>
    }
}

The above same can achieved through Component as well. Need to wrap LazyLoad on top of the component for lazyloading

import { LazyLoad } from 'react-observer-api';

export default () => {
    
    return {
        <LazyLoad>
            <>...Component goes here....</>
        </LazyLoad>
    }
}

import { LazyLoad } from 'react-observer-api';

export default () => {
    const style = {
        padding: 10
    };
    return {
        <LazyLoad as="span" style={style} forceVisible>
            <>...Component goes here....</>
        </LazyLoad>
    }
}

For IE support, need to add polyfill

You can import the polyfill directly or use a service like polyfill.io to add it when needed.

npm i intersection-observer

Then import it in your app:

import 'intersection-observer'

If you are using Webpack (or similar) you could use dynamic imports, to load the Polyfill only if needed. A basic implementation could look something like this:

    /**
    * Do feature detection, to figure out which polyfills needs to be imported.
    **/
    async function loadPolyfills() {
        if (typeof window.IntersectionObserver === 'undefined') {
            await import('intersection-observer')
        }
    }

MIT