NOTE FROM MAINTAINER:

This library is no more required nowadays, you can now rely on the Intersection Observer API which is available in all modern browsers: https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API

/NOTE FROM MAINTAINER

inViewport

Know when an element is in the window viewport or a custom viewport.

API

Immediate result

var inViewport = require('in-viewport');
var elem = document.getElementById('myFancyDiv');

var isInViewport = inViewport(elem); // returns `true` or `false`

alert('myFancyDiv is ' + isInViewport ? 'visible' : 'not visible' + ' in the window');

Using a callback

We watch for your element to enters the viewport and call your callback when it does.

var inViewport = require('in-viewport');
var elem = document.getElementById('myFancyDiv');

inViewport(elem, visible);

function visible(elt) {
  // elt === elem
  alert(elt.id + ' is visible in the window!');
}

The first callback argument is always the element that entered the viewport.

Callback watcher API

The callback is called only one time, when the element is in the viewport for the first time. At any time you can rewatch or stop watching, by using the watch and dispose API.

var inViewport = require('in-viewport');
var elem = document.getElementById('myFancyDiv');
var count = 0;
var timer;

var watcher = inViewport(elem, visible);

function visible() {
  count++;
  timer = setTimeout(watcher.watch, 1000);
}

setTimeout(function(){
  watcher.dispose();
  clearTimeout(timer);
  alert('myfancyDiv was visible '+count+' seconds in the last 10 seconds!');
}, 10000);

A custom container

By default, we use the current window as the reference viewport. But you can also specify another element as a reference viewport.

var inViewport = require('in-viewport');
var customContainer = document.getElementById('myFancyContainer');
var elem = document.getElementById('myFancyDiv');

inViewport(elem, { container: customContainer }, visible);

function visible() {
  alert('myfancyDiv is visible in the `customContainer`!');
}

Specifying an offset

By default, when your element precisely enters the viewport, you get a callback.

But maybe you want to know when your element is soon-to-be-shown in the viewport?

Use the offset param for that!

var inViewport = require('in-viewport');
var elem = document.getElementById('myFancyDiv');

inViewport(elem, { offset: 300 }, visible);

function visible() {
  alert('myfancyDiv is visible in the `customContainer`!');
}

When your element is near 300px of the viewport, you get your callback / true result.

Specifying debounce value

Currently, scroll and resize events are called every 15ms, but there are situations where larger value like 300ms is more sensible, e.g. image lazyload, where you probably want to wait for user to stop with scrolling before loading every image that comes into viewport.

You can change that with debounce param.

var inViewport = require('in-viewport');
var elem = document.getElementById('myFancyDiv');

inViewport(elem, { debounce: 300 }, visible);

function visible() {
  alert('myfancyDiv is visible in the `customContainer`!');
}

Failsafe check

By default, inViewport does a failsafe to handle display manipulation that does not throw an event. It works with a setInterval performed every 150ms.

One of the situations where this is useful is when you have a hidden parent containing elements; when the parent becomes visible, we have no event that the children became visible. If you handle cases like this by yourself in different part of your codebase (e.g. you have callback which is active when parent becomse visible), you can turn it off with failsafe param.

var inViewport = require('in-viewport');
var elem = document.getElementById('myFancyDiv');

inViewport(elem, { failsafe: false }, visible);

function visible() {
  alert('myfancyDiv is visible in the `customContainer`!');
}

Dynamic element creation (document.createElement)

If you are creating elements dynamically, be sure to call inViewport when the element is in the DOM.

Otherwise it may fail on old browsers.

We check for newly visible elements on scroll or resize.

We use MutationObserver to listen for newly added DOM nodes that were previously registered with in-viewport.

MutationObserver is not compatible with old browsers.

That is why, if you need old browsers full compatibility, you should call in-viewport after inserting elements in the DOM.

Use cases

Images, iframes, widgets lazyloader
infinite scroll
loading widgets only when needed

Quirksmode

Be sure to be in standards-compliant mode.

Quirks mode is not supported since most browsers will report invalid values for window viewport.

Developing

Launch the dev server:

npm run dev

Browse to http://localhost:8080/__zuul.

Tests are written with mocha.

Building

We provide a pre-built version of in-viewport in build/in-viewport.min.js.

But you can build your own:

npm run build

You get the build in build/in-viewport.min.js.

Please consider using browserify.

License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

vvo/in-viewport