ember-in-viewport
Detect if an Ember View or Component is in the viewport @ 60FPS
ember-in-viewport is built and maintained by DockYard, contact us for expert Ember.js consulting.
Read the blogpost
This Ember addon adds a simple, highly performant Service or modifier to your app. This library will allow you to check if a Component
or DOM element has entered the browser's viewport. By default, this uses the IntersectionObserver
API if it detects it the DOM element is in your user's browser – failing which, it falls back to using requestAnimationFrame
, then if not available, the Ember run loop and event listeners.
We utilize pooling techniques to reuse Intersection Observers and rAF observers in order to make your app as performant as possible and do as little works as possible.
Demo or examples
Table of Contents
Installation
ember install ember-in-viewport
Usage
Usage is simple. First, inject the service to your component and start "watching" DOM elements.
import Component from '@glimmer/component';
import { action } from '@ember/object';
import { inject as service } from '@ember/service';
export default class MyClass extends Component {
@service inViewport
@action
setupInViewport() {
const loader = document.getElementById('loader');
const viewportTolerance = { bottom: 200 };
const { onEnter, _onExit } = this.inViewport.watchElement(loader, { viewportTolerance });
onEnter(this.didEnterViewport.bind(this));
}
didEnterViewport() {
this.infinityLoad();
}
willDestroy() {
const loader = document.getElementById('loader');
this.inViewport.stopWatching(loader);
super.willDestroy(...arguments);
}
}
<ul>
<li></li>
...
</ul>
<div id="loader"></div>
You can also use Modifiers
as well. Using modifiers cleans up the boilerplate needed and is shown in a later example.
Configuration
To use with the service based approach, simply pass in the options to watchElement
as the second argument.
import Component from '@glimmer/component';
import { inject as service } from '@ember/service';
export default class MyClass extends Component {
@service inViewport
@action
setupInViewport() {
const loader = document.getElementById('loader');
const { onEnter, _onExit } = this.inViewport.watchElement(
loader,
{
viewportTolerance: { bottom: 200 },
intersectionThreshold: 0.25,
scrollableArea: '#scrollable-area'
}
);
}
}
Global options
You can set application wide defaults for ember-in-viewport
in your app (they are still manually overridable inside of a Component). To set new defaults, just add a config object to config/environment.js
, like so:
module.exports = function(environment) {
var ENV = {
viewportConfig: {
viewportUseRAF : true,
viewportSpy : false,
viewportListeners : [],
intersectionThreshold : 0,
scrollableArea : null,
viewportTolerance: {
top : 0,
left : 0,
bottom : 0,
right : 0
}
}
};
};
Modifiers
Using with Modifiers is easy.
You can either use our built in modifier {{in-viewport}}
or a more verbose, but potentially more flexible generic modifier. Let's start with the former.
- Use
{{in-viewport}}
modifier on target element - Ensure you have a callbacks in context for enter and/or exit
options
are optional - see Advanced usage (options)
<ul class="list">
<li></li>
<li></li>
<div {{in-viewport onEnter=(fn this.onEnter artwork) onExit=this.onExit scrollableArea=".list"}}>
List sentinel
</div>
</ul>
This modifier is useful for a variety of scenarios where you need to watch a sentinel. With template only components, functionality like this is even more important! If you have logic that currently uses the did-insert
modifier to start watching an element, try this one out!
If you need more than our built in modifier...
- Install @ember/render-modifiers
- Use the
did-insert
hook inside a component - Wire up the component like so
Note - This is in lieu of a did-enter-viewport
modifier, which we plan on adding in the future. Compared to the solution below, did-enter-viewport
won't need a container (this
) passed to it. But for now, to start using modifiers, this is the easy path.
import Component from '@glimmer/component';
import { action } from '@ember/object';
import { inject as service } from '@ember/service';
export default class MyClass extends Component {
@service inViewport
@action
setupInViewport() {
const loader = document.getElementById('loader');
const viewportTolerance = { bottom: 200 };
const { onEnter, _onExit } = this.inViewport.watchElement(loader, { viewportTolerance });
onEnter(this.didEnterViewport.bind(this));
}
didEnterViewport() {
this.infinityLoad();
}
willDestroy() {
const loader = document.getElementById('loader');
this.inViewport.stopWatching(loader);
super.willDestroy(...arguments);
}
}
<div {{did-insert this.setupInViewport}}>
{{yield}}
</div>
Options as the second argument to inViewport.watchElement
include:
-
intersectionThreshold: decimal or array
Default: 0
A single number or array of numbers between 0.0 and 1.0. A value of 0.0 means the target will be visible when the first pixel enters the viewport. A value of 1.0 means the entire target must be visible to fire the didEnterViewport hook.
Similarily, [0, .25, .5, .75, 1] will fire didEnterViewport every 25% of the target that is visible.
(https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API#Thresholds)
Some notes:
- If the target is offscreen, you will get a notification via
didExitViewport
that the target is initially offscreen. Similarily, this is possible to notify if onscreen when your site loads. - If intersectionThreshold is set to anything greater than 0, you will not see
didExitViewport
hook fired due to our use of the isIntersecting
property. See last comment here: https://bugs.chromium.org/p/chromium/issues/detail?id=713819 for purpose of isIntersecting
- To get around the above issue and have
didExitViewport
fire, set your intersectionThreshold
to [0, 1.0]
. When set to just 1.0
, when the element is 99% visible and still has isIntersecting as true, when the element leaves the viewport, the element isn't applicable to the observer anymore, so the callback isn't called again. - If your intersectionThreshold is set to 0 you will get notified if the target
didEnterViewport
and didExitViewport
at the appropriate time.
-
scrollableArea: string | HTMLElement
Default: null
A CSS selector for the scrollable area. e.g. ".my-list"
-
viewportSpy: boolean
Default: false
viewportSpy: true
is often useful when you have "infinite lists" that need to keep loading more data.
viewportSpy: false
is often useful for one time loading of artwork, metrics, etc when the come into the viewport.
If you support IE11 and detect and run logic onExit
, then it is necessary to have this true
to that the requestAnimationFrame watching your sentinel is not torn down.
When true
, the library will continually watch the Component
and re-fire hooks whenever it enters or leaves the viewport. Because this is expensive, this behaviour is opt-in. When false, the intersection observer will only watch the Component
until it enters the viewport once, and then it unbinds listeners. This reduces the load on the Ember run loop and your application.
NOTE: If using IntersectionObserver (default), viewportSpy wont put too much of a tax on your application. However, for browsers (Safari < 12.1) that don't currently support IntersectionObserver, we fallback to rAF. Depending on your use case, the default of false
may be acceptable.
-
viewportTolerance: object
Default: { top: 0, left: 0, bottom: 0, right: 0 }
This option determines how accurately the Component
needs to be within the viewport for it to be considered as entered. Add bottom margin to preemptively trigger didEnterViewport.
For IntersectionObserver, this property interpolates to rootMargin.
For rAF, this property will use bottom
tolerance and measure against the height of the container to determine when to trigger didEnterViewport.
Also, if your sentinel (the watched element) is a zero-height element, ensure that the sentinel actually is able to enter the viewport.
Out of the box
Chrome | 51 [1] |
Firefox (Gecko) | 55 [2] |
MS Edge | 15 |
Internet Explorer | Not supported |
Opera [1] | 38 |
Safari | Safari Technology Preview |
Chrome for Android | 59 |
Android Browser | 56 |
Opera Mobile | 37 |
- [1] Reportedly available, it didn't trigger the events on initial load and lacks
isIntersecting
until later versions. - [2] This feature was implemented in Gecko 53.0 (Firefox 53.0 / Thunderbird 53.0 / SeaMonkey 2.50) behind the preference
dom.IntersectionObserver.enabled
.
Running
Running Tests
ember test
ember test --serve
Building
For more information on using ember-cli, visit http://www.ember-cli.com/.
Legal
DockYard, Inc © 2015
@dockyard
Licensed under the MIT license
Contributors
We're grateful to these wonderful contributors who've contributed to ember-in-viewport
: