React Waypoint
A React component to execute a function whenever you scroll to an element. Works in all containers that can scroll, including the window.
React Waypoint can be used to build features like lazy loading content, infinite scroll, scrollspies, or docking elements to the viewport on scroll.
Inspired by Waypointswaypoints, except this little library grooves the Reactreact way.
Demo
View demo pagedemo-page
Installation
npm
npm install react-waypoint --save
yarn
yarn add react-waypoint
Usage
import { Waypoint } from 'react-waypoint';
<Waypoint
onEnter={this._handleWaypointEnter}
onLeave={this._handleWaypointLeave}
/>
A waypoint normally fires
onEnter
and onLeave
as you are scrolling, but it
can fire because of other events too:- When the window is resized
- When it is mounted (fires
onEnter
if it's visible on the page) - When it is updated/re-rendered by its parent
Callbacks will only fire if the new position changed from the last known position. Sometimes it's useful to have a waypoint that fires
onEnter
every
time it is updated as long as it stays visible (e.g. for infinite scroll). You
can then use a key
prop to control when a waypoint is reused vs. re-created.<Waypoint
key={cursor}
onEnter={this._loadMoreContent}
/>
Alternatively, you can also use an
onPositionChange
event to just get
notified when the waypoint's position (e.g. inside the viewport, above or
below) has changed.<Waypoint
onPositionChange={this._handlePositionChange}
/>
Waypoints can take a child, allowing you to track when a section of content enters or leaves the viewport. For details, see Children, below.
<Waypoint onEnter={this._handleEnter}>
<div>
Some content here
</div>
</Waypoint>
Example: JSFiddle Examplejsfiddle-example
Prop types
propTypes: {
/**
* Function called when waypoint enters viewport
*/
onEnter: PropTypes.func,
/**
* Function called when waypoint leaves viewport
*/
onLeave: PropTypes.func,
/**
* Function called when waypoint position changes
*/
onPositionChange: PropTypes.func,
/**
* Whether to activate on horizontal scrolling instead of vertical
*/
horizontal: PropTypes.bool,
/**
* `topOffset` can either be a number, in which case its a distance from the
* top of the container in pixels, or a string value. Valid string values are
* of the form "20px", which is parsed as pixels, or "20%", which is parsed
* as a percentage of the height of the containing element.
* For instance, if you pass "-20%", and the containing element is 100px tall,
* then the waypoint will be triggered when it has been scrolled 20px beyond
* the top of the containing element.
*/
topOffset: PropTypes.oneOfType([
PropTypes.string,
PropTypes.number,
]),
/**
* `bottomOffset` can either be a number, in which case its a distance from the
* bottom of the container in pixels, or a string value. Valid string values are
* of the form "20px", which is parsed as pixels, or "20%", which is parsed
* as a percentage of the height of the containing element.
* For instance, if you pass "20%", and the containing element is 100px tall,
* then the waypoint will be triggered when it has been scrolled 20px beyond
* the bottom of the containing element.
*
* Similar to `topOffset`, but for the bottom of the container.
*/
bottomOffset: PropTypes.oneOfType([
PropTypes.string,
PropTypes.number,
]),
/**
* Scrollable Ancestor - A custom ancestor to determine if the
* target is visible in it. This is useful in cases where
* you do not want the immediate scrollable ancestor to be
* the container. For example, when your target is in a div
* that has overflow auto but you are detecting onEnter based
* on the window.
*
* This should typically be a reference to a DOM node, but it will also work
* to pass it the string "window" if you are using server rendering.
*/
scrollableAncestor: PropTypes.any,
/**
* fireOnRapidScroll - if the onEnter/onLeave events are to be fired
* on rapid scrolling. This has no effect on onPositionChange -- it will
* fire anyway.
*/
fireOnRapidScroll: PropTypes.bool,
/**
* Use this prop to get debug information in the console log. This slows
* things down significantly, so it should only be used during development.
*/
debug: PropTypes.bool,
},
All callbacks (
onEnter
/onLeave
/onPositionChange
) receive an object as the
only argument. That object has the following properties:currentPosition
- the position that the waypoint has at the moment. One
Waypoint.below
, Waypoint.above
, Waypoint.inside
,
and Waypoint.invisible
.previousPosition
- the position that the waypoint had before. Also one
Waypoint.below
, Waypoint.above
, Waypoint.inside
,
and Waypoint.invisible
.In most cases, the above two properties should be enough. In some cases though, you might find these additional properties useful:
event
- the native scroll
waypointTop
- the waypoint's distance to the top of the viewport.viewportTop
- the distance from the scrollable ancestor to the
viewportBottom
- the distance from the bottom of the scrollable
If you use es6 object destructuring, this means that you can use waypoints in the following way:
<Waypoint onEnter={({ previousPosition, currentPosition, event }) => {
// do something useful!
}}
/>
If you are more familiar with plain old js functions, you'll do something like this:
<Waypoint onEnter={function(props) {
// here you can use `props.currentPosition`, `props.previousPosition`, and
// `props.event`
}}
/>
Offsets and Boundaries
Two of the Waypoint props aretopOffset
and bottomOffset
. To appreciate
what these can do for you, it will help to have an understanding of the
"boundaries" used by this library. The boundaries of React Waypoint are the top
and bottom of the element containing your scrollable content (although this element
can be configured). When a
waypoint is within these boundaries, it is considered to be "inside." When a
waypoint passes beyond these boundaries, then it is "outside." The onEnter
and
onLeave
props are called as an element transitions from being inside to
outside, or vice versa.The
topOffset
and bottomOffset
properties can adjust the placement of these
boundaries. By default, the offset is '0px'
. If you specify a positive value,
then the boundaries will be pushed inward, toward the center of the page. If
you specify a negative value for an offset, then the boundary will be pushed
outward from the center of the page.Here is an illustration of offsets and boundaries. The black box is the
scrollableAncestor
. The pink
lines represent the location of the boundaries. The offsets that determine
the boundaries are in light pink.Horizontal Scrolling Offsets and Boundaries
By default, waypoints listen to vertical scrolling. If you want to switch to horizontal scrolling instead, use thehorizontal
prop. For simplicity's sake,
all other props and callbacks do not change. Instead, topOffset
and
bottomOffset
(among other directional variables) will mean the offset from
the left and the offset from the right, respectively, and work exactly as they
did before, just calculated in the horizontal direction.Example Usage
Positive values of the offset props are useful when you have an element that overlays your scrollable area. For instance, if your app has a50px
fixed
header, then you may want to specify topOffset='50px'
, so that the
onEnter
callback is called when waypoints scroll into view from beneath the
header.Negative values of the offset prop could be useful for lazy loading. Imagine if you had a lot of large images on a long page, but you didn't want to load them all at once. You can use React Waypoint to receive a callback whenever an image is a certain distance from the bottom of the page. For instance, by specifying
bottomOffset='-200px'
, then your onEnter
callback would be called when
the waypoint comes closer than 200 pixels from the bottom edge of the page. By
placing a waypoint near each image, you could dynamically load them.There are likely many more use cases for the offsets: be creative! Also, keep in mind that there are two boundaries, so there are always two positions when the
onLeave
and onEnter
callback will be called. By using the arguments
passed to the callbacks, you can determine whether the waypoint has crossed the
top boundary or the bottom boundary.Children
If you don't pass a child into your Waypoint, then you can think of the waypoint as a line across the page. Whenever that line crosses a boundary, then theonEnter
or onLeave
callbacks
will be called.If you do pass a child, it can be a single DOM component (e.g.
<div>
) or a
composite component (e.g. <MyComponent />
).Waypoint needs a DOM node to compute its boundaries. When you pass a DOM component to Waypoint, it handles getting a reference to the DOM node through the
ref
prop automatically.If you pass a composite component, you can wrap it with
React.forwardRef
(requires react@^16.3.0
)
and have the ref
prop being handled automatically for you, like this:class Block extends React.Component {
render() {
return <div ref={this.props.innerRef}>Hello</div>
}
}
const BlockWithRef = React.forwardRef((props, ref) => {
return <Block innerRef={ref} {...props} />
})
const App = () => (
<Waypoint>
<BlockWithRef />
</Waypoint>
)
If you can't do that because you are using older version of React then you need to make use of the
innerRef
prop passed by Waypoint to your component.
Simply pass it through as the ref
of a DOM component and you're all set. Like in
this example:class Block extends React.Component {
render() {
return <div ref={this.props.innerRef}>Hello</div>
}
}
Block.propTypes = {
innerRef: PropTypes.func.isRequired,
}
const App = () => (
<Waypoint>
<Block />
</Waypoint>
)
The
onEnter
callback will be called when any part of the child is visible
in the viewport. The onLeave
callback will be called when all of the child
has exited the viewport.(Note that this is measured only on a single axis. What this means is that for a Waypoint within a vertically scrolling parent, it could be off of the screen horizontally yet still fire an onEnter event, because it is within the vertical boundaries).
Deciding whether to pass a child or not will depend on your use case. One example of when passing a child is useful is for a scrollspy (like Bootstrap's). Imagine if you want to fire a waypoint when a particularly long piece of content is visible onscreen. When the page loads, it is conceivable that both the top and bottom of this piece of content could lie outside of the boundaries, because the content is taller than the viewport. If you didn't pass a child, and instead put the waypoint above or below the content, then you will not receive an
onEnter
callback (nor any other callback from this library).
Instead, passing this long content as a child of the Waypoint would fire the onEnter
callback when the page loads.Containing elements and scrollableAncestor
React Waypoint positions its boundaries based on the
first scrollable ancestor of the Waypoint.If that algorithm doesn't work for your use case, then you might find the
scrollableAncestor
prop useful. It allows you to specify what the scrollable
ancestor is. Pass a reference to a DOM node as that prop, and the Waypoint will
use the scroll position of that node, rather than its first scrollable
ancestor.This can also be the string "window", which can be useful if you are using server rendering.
Example Usage
Sometimes, waypoints that are deeply nested in the DOM tree may need to track the scroll position of the page as a whole. If you want to be sure that no other scrollable ancestor is used (since, once again, the first scrollable ancestor is what the library will use by default), then you can explicitly set thescrollableAncestor
to be the window
to ensure that no other element is used.This might look something like:
<Waypoint
scrollableAncestor={window}
onEnter={this._handleWaypointEnter}
onLeave={this._handleWaypointLeave}
/>
Troubleshooting
If your waypoint isn't working the way you expect it to, there are a few ways you can debug your setup.OPTION 1: Add the
debug={true}
prop to your waypoint. When you do, you'll see console
logs informing you about the internals of the waypoint.OPTION 2: Clone and modify the project locally.
- clone this repo
- add
console.log
or breakpoints where you think it would be useful. npm link
in the react-waypoint repo.npm link react-waypoint
in your project.- if needed rebuild react-waypoint module:
npm run build-npm
Limitations
In this component we make a few assumptions that we believe are generally safe, but in some situations might present limitations.- We determine the scrollable-ness of a node by inspecting its computed
- We assume that waypoints are rendered within at most one scrollable container.
- We also base the visibility calculations on the scroll position of the
window
if no scrollable container is found). This
means that if your scrollable container has a height that is greater than the
window, it might trigger onEnter
unexpectedly.In the wild
Organizations and projects usingreact-waypoint
.Credits
Credit to trotzigtrotzig-github and lencionilencioni-github for writing this component, and Brigadebrigade-home for open sourcing it.Thanks to the creator of the original Waypoints library, imakewebthingsimakewebthings-github.
License
MITmit-licenseMake sure to check out other popular open-source tools from the Brigadeciviccc-github team: dock, overcommit, haml-lint, and scss-lint.