React component using the browser's Intersection Observer API to watch for when an element is within (or intersecting with) the viewport.
npm install react-observed  
React component using the browser's Intersection Observer API to watch for when an element is within (or intersecting with) the viewport.
``
npm install react-observed --save
or with Yarn
`
yarn add react-observed
Note: For complete browser support you must also provide an Intersection Observer polyfill.
`
npm install intersection-observer --save
or
`
yarn add intersection-observer
takes a function as a child which gives you access to the isInView and mapRef properties.
mapRef is the ref function callback that must be declared on the observed target element like
. Then isInView will give you the current state of the observed element.Here's an example:
`jsx
{({ isInView, mapRef }) => (
{isInView ? (
I'm in view!
) : (
I'm not in view
)}
)}
`\ Props
takes the props as shown by the following example:`jsx
false
intersectionRatio={0.5} // target's visibility must pass the 50% threshold to be considered visible
once // discontinue observing the target once it's become visible
onChange={isInView => {}} // handler called with the current state whenever it changes
onEnter={() => {}} // handler called when the observed element enters
onExit={() => {}} // handler called when the observed element exits
onIntersect={entry => {}} // handler called when each threshold is met with the entry data
options={{
// IntersectionObserver constuctor options
root: null,
rootMargin: "0px",
threshold: 0.5
}}
/>
`| Name | Type | Default | Description |
| --------------------- | :--------: | :---------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| initialViewState |
| false | Optionally sets the initial isInView state. By default this is false until the observer updates the state. |
| intersectionRatio | Number | 0 | The intersection ratio (a value between 0–1) that when >= to the target's intersect ratio and not equal to 0 will be considered in view. |
| once | Boolean | false | If once is true the observer will disconnect after the target element has entered the view. Useful for triggering something when in view for a single time. |
| onChange | Function | | Handler to be called with the current isInView state whenever it changes. |
| onEnter | Function | | Handler to be called when the isInView state changes to true. |
| onExit | Function | | Handler to be called when the isInView state changes to false. |
| onIntersect | Function | | Handler to be called when each threshold is met with the current entry data. |
| options | Object | \*see below | Options passed to the IntersectionObserver constructor. |$3
These are the options passed to the IntersectionObserver constructor. The default
options to the component are:`js
options: {
root: null,
rootMargin: '0px',
threshold: [0],
}
`The following is as described on MDN:
| Name | Type | Default | Description |
| -------------- | :-----------------: | :------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| root |
| null | The DOM element that is used as the viewport for checking visiblity of the target. Must be the ancestor of the target. Defaults to the browser viewport if not specified or if null. |
| rootMargin | String | 0px | Margin around the root. Can have values similar to the CSS margin property, e.g. 10px 20px 30px 40px (top, right, bottom, left). If the root element is specified, the values can be percentages. This set of values serves to grow or shrink each side of the root element's bounding box before computing intersections. Defaults to all zeros. |
| threshold | Number or Array | [0] | Either a single Number or an Array of numbers which indicate at what percentage of the target's visibility the observer's callback should be executed. If you only want to detect when visibility passes the 50% mark, you can use a value of 0.5. If you want the callback run every time visibility passes another 25%, you would specify the array [0, 0.25, 0.5, 0.75, 1]. The default is 0 (meaning as soon as even one pixel is visible, the callback will be run). A value of 1.0 means that the threshold isn't considered passed until every pixel is visible. |Render Callback
The child function takes one object parameter like such
{ isInView, mapRef }. It's required to map a ref function to a DOM element otherwise will throw an error.Example:
`jsx
{({ mapRef }) => }
`The keys of which are:
| Name | Type | Description |
| ------------ | :--------: | --------------------------------------------------------------------------------------------------------------------------------------- |
| isInView |
| This is true when the observed element's intersection ratio is >= to the intersectionRatio prop. |
| mapRef | Function | This a function that is declared as the ref` of the DOM element to be observed. Note that this is required for the observer to work. |Intersection Observer is pretty well supported by major browsers, with the exception of Safari/iOS Safari. There's also not been much movement by the Safari team to add support. This is unfortunate but adding a good polyfill will work great for adding support to Safari or IE11. You can track Safari's lack of progress here.