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https://github.com/vvo/in-viewport

Get a callback when any element becomes visible in a viewport (body or custom viewport)
https://github.com/vvo/in-viewport

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Get a callback when any element becomes visible in a viewport (body or custom viewport)

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**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 [![devDependency Status](http://img.shields.io/david/dev/vvo/in-viewport.svg?style=flat-square)](https://david-dm.org/vvo/in-viewport#info=devDependencies)



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



[![Selenium Test Status](https://saucelabs.com/browser-matrix/in-viewportvvo.svg)](https://saucelabs.com/u/in-viewportvvo)



## API



### Immediate result



```js

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.



```js

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.



```js

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.



```js

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!



```js

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.



```js

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.



```js

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](https://developer.mozilla.org/en-US/docs/Web/API/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](http://github.com/vvo/lazyload)

* infinite scroll

* loading widgets only when needed



## Quirksmode



Be sure to be in [standards-compliant mode](http://en.wikipedia.org/wiki/HTML5#Markup).



[Quirks mode](http://en.wikipedia.org/wiki/Quirks_mode) is not supported since most browsers

will report invalid values for window viewport.



## Developing



Launch the dev server:



```shell

npm run dev

```



Browse to [http://localhost:8080/__zuul](http://localhost:8080/__zuul).



[Tests](test/) are written with [mocha](https://github.com/visionmedia/mocha).



## Building



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



But you can build your own:



```shell

npm run build

```



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



Please consider using [browserify](https://github.com/substack/node-browserify).



## License



Copyright (c) 2013-2016 Vincent Voyer



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.