react-intersection-observer

@shopify/react-intersection-observer

A React wrapper around the IntersectionObserver API.

Installation

$ yarn add @shopify/react-intersection-observer

Usage

useIntersection(options: Options)

The useIntersection hook takes in IntersectionObserver options, and returns a tuple of:

• The state of the observer.
• An object that you can pass as a ref to the DOM element you wish to track.

function MyComponent() {
  const [intersection, intersectionRef] = useIntersection();

  return (
    <div ref={intersectionRef}>Intersection: {intersection.isIntersecting}</div>
  );
}

You can pass additional options to this hook that are used to create the underlying IntersectionObserver:

• threshold: a number or array of number indicating the intersectionRatio that must be met before the observer is triggered.
• root: a string or element that is used as the viewport for visibility testing. If a string is passed, it will be treated as a selector.
• rootMargin: a string representing the margins by which to shrink the root’s bounding box before computing intersections.

<IntersectionObserver />

This package also exports an IntersectionObserver component, which is a fairly minimal component wrapper around the useIntersection hook, and accepts the same threshold, root, and rootMargin values as props. The onIntersectionChange prop you pass to this component will be called with an IntersectionObserverEntry object, which describes the state of the intersection (and is equivalent to the first value of the tuple returned from the hook).

Unlike the useIntersection hook, this component will create its own DOM node that will be observed, rather than requiring you to pass a ref to a DOM node you already control. You can customize the rendered markup by passing either of the following props:

• children, which will be rendered inside of the node being observed for intersections.
• wrapperComponent, which changes the DOM node being wrapped around those children (defaults to a div).

<div ref={this.parentElement}>
  <IntersectionObserver
    root={this.parentElement.current}
    rootMargin="10px 10%"
    threshold={1}
    onIntersecting={entry => console.log('intersectionRatio > 0', entry)}
    onNotIntersecting={entry => console.log('intersectionRatio = 0', entry)}
  />
</div>

Lifecycle

When useIntersection is passed new options (or, when IntersectionObserver receives new props), this library will do the minimum amount of work to unobserve/ re-observe with the new fields. The most expensive updates to make are changing threshold, root, rootMargin, and, in the case of the component version, wrapperComponent, as these require disconnecting the old observer and recreating a new one.

When a component consuming the useIntersection hook is unmounted, the intersection observer is disconnected. The same applies if you unmount an IntersectionObserver component.

Browser support

To polyfill IntersectionObserver, please use the @shopify/polyfills/intersection-observer package.

If you do not polyfill the feature and it is not supported in the current browser, the useIntersection hook and the IntersectionObserver component will decide what to do based on the unsupportedBehavior option. This value should be a member of the UnsupportedBehavior enum (exported from this package). Currently, there are two options:

• UnsupportedBehavior.TreatAsIntersecting: immediately sets state/ calls onIntersectionChange on mount with a non-0 intersectionRatio (this is the default).
• UnsupportedBehavior.Ignore: never calls marks the intersection observer as being intersecting.