ScrollMonitor-React

This is a React component that provides an API to the scrollMonitor. It lets you create both watchers and scroll containers.

There is now a React hooks version.

It adds all the boolean properties from a watcher to this.props and takes all the method properties as properties.

Scrollmonitor-react is two higher order components. They're functions that you pass an original component and receive a new component that adds functionality to the original.

Basic Usage

Knowing when you're in the viewport

import React from 'react';
import { Watch } from 'scrollmonitor-react';

export default Watch(class MyComponent extends React.Component {

	render () {
		var text;
		if (this.props.isInViewport) {
			text = 'I AM in the viewport!';
		} else {
			text = 'You will never see this because it gets replaced when it enters the viewport.'
		}

		return (<span>
			{text}
			{this.props.children}
		</span>);
	}
});

Doing something when a watched child enters or exits the viewport

Provide methods with the scrollMonitor event names as props to your component.

import React from 'react';

import MyWatchedComponent from './the/example/above';

export default MyParentComponent extends React.Component {

	receiveStateChange (watcher) {
		console.log('state changed!', watcher)
	}

	render () {
		return (<MyWatchedComponent stateChange={this.receiveStateChange} />)
	}
}

Avoid starting the watcher automatically

By default the watcher is started on every enhanced component, but there can be situations where you want to start the watcher later so you can set the prop autoStart to false to avoid starting the watcher automatically.

API

this.props provided to your component

• this.props.isInViewport - true if any part of the element is visible, false if not.
• this.props.isFullyInViewport - true if the entire element is visible [1].
• this.props.isAboveViewport - true if any part of the element is above the viewport.
• this.props.isBelowViewport - true if any part of the element is below the viewport.
• this.props.lockWatcher() - locks the watcher letting you move the element but watch the same place. See the scrollMonitor's documentation for more info.
• this.props.unlockWatcher() - unlocks the watcher.
• this.props.startWatcher() - starts the watcher if it's not running
• this.props.stopWatcher() - stops the watcher if it's running

1. If the element is larger than the viewport isFullyInViewport is true when the element spans the entire viewport.

Properties you provide to the component

<MyWatchedComponent
	autoStart={true|false} // Decide if watcher should start when component is mounted. Default: true
	innerRef={(el, watcher, props) => this.foo = el} // allows you to gain access to the DOM element, the watcher, and the child's props
	stateChange={(watcher, childProps) => {}} // Called when any part of the state changes.
	visibilityChange={(watcher, childProps) => {}} // when the element partially enters or fully exits the viewport.
	enterViewport={(watcher, childProps) => {}} // when the element enters the viewport.
	fullyEnterViewport={(watcher, childProps) => {}} // when the element is completely in the viewport [1].
	exitViewport={(watcher, childProps) => {}} // when the element completely leaves the viewport.
	partiallyExitViewport={(watcher, childProps) => {}} // when the element goes from being fully in the viewport to only partially [2]
>
	<h1>Child components are fine too.</h1>
</MyWatchedComponent>

All callbacks receive two arguments: the watcher and the props of the child.

1. If the element is larger than the viewport fullyEnterViewport will be triggered when the element spans the entire viewport. 2. If the element is larger than the viewport partiallyExitViewport will be triggered when the element no longer spans the entire viewport.

Scroll Containers

The ScrollContainer HOC lets you create scrollMonitor Scroll Containers. It provides a scroll container on this.props that it must pass to its children.

import React from 'react';
import { render } from 'react-dom';
import { ScrollContainer } from 'scrollmonitor-react';

import MyWatchedContainer from 'the/example/above';

// Your container gets this.props.scrollContainer, which it must pass to the child components.
var Container = ScrollContainer(ContainerComponent extends React.Component {
	render () {
		i = 1;
		return (<div className="container-scroll">
			<MyWatchedContainer scrollContainer={this.props.scrollContainer}>{i++}</MyWatchedContainer>
			{...times a million}
		</div>);
	}
}