Am I Visible?

AMIVisible (or simply AMI for close friends) is a dependency-free micro tool (735 bytes min+gz) written in vanilla JavaScript for checking when an element appears or disappears from the viewport.

AMI implements throttling mechanisms in order to not flood the main JS thread on scroll events and also supports event delegation.

Installation

Run bower install --save amivisible
Add the script tag <script src="bower_components/amivisible/lib/bundle.min.js"></script>
You are ready to go!

API

`AMIVisible.monitor`

The main method to start monitoring an element.

AMIVisible.monitor(element, options);

Options

key	type	default	description
force_process	boolean	false	Checks the element state immediately without waiting for next scroll event
enable_bubbling	boolean	false	Enabled event bubbling for Event Delegation

`AMIVisible.set`

Change the default AMI's internal options.

AMIVisible.set(key, newValue);

Available settings

key	type	default	description
throttle_window	Number	90	The window (in milliseconds) before making a new scroll calculation

Usage

Basic usage

var element = document.getElementById('fancy-element');

element.addEventListener('appear', function() {
  console.log('element appeared on the screen!');
});

element.addEventListener('disappear', function() {
  console.log('element vanished from the screen!');
});

AMIVisible.monitor(element);

Advanced usage (Event Delegation)

var element = document.getElementById('fancy-element');

document.body.addEventListener('appear', function(event) {
  if(event.target === element) {
    console.log('element appeared on the screen!');
  }
});

document.body.addEventListener('disappear', function(event) {
  if(event.target === element) {
    console.log('element vanished from the screen!');
  }
});

AMIVisible.monitor(element, {
  force_process: true, // immediately checks if the element is visible or not
  enable_bubbling: true // bubbles the event, useful for event delegation
});

Known issues

There is currently no way to stop monitoring an object.
There is no way to change the scroll parent for specific elements. We can only check for window scroll now.

Compatibility

Tested on Chrome, Firefox and Safari

vinerz/amivisible