content-observer

Watch one or more targets position for when they intersect a defined point in the viewport. Uses the Intersection Observer API

Demo

https://tflx.github.io/content-observer

Features

• Supports vertical and horizontal scrolling
• Define a point in pixels or a percentage of the screen height/width
• Re-calculates on browser resize
• Update hash-location automatically - requires id on the target(s)
• Disconnect to stop watching targets

Installation

<script src="dist/main.js"></script>

ContentObserver will be available in the global scope.

Or install via NPM/Yarn and require as a module

Install using Yarn:

yarn add content-observer

or NPM:

npm install content-observer --save

Usage

import ContentObserver from 'content-observer';
 
class App {
  constructor() {
    const co = new ContentObserver(document.querySelectorAll('.observe'), {
      callback: this.handleCallback,
      offset: 200, //or fx. '50%'
      enableLocationHash: true,
      direction: 'vertical'
    });
  }
 
  handleCallback(target, inView) {
    if (inView) document.querySelector('header').innerHTML = target.id.toUpperCase();
  }
}
 
export default new App;

The constructor accepts two arguments: the targets (required) to watch and an options object.

To stop watching target(s):

co.disconnect()

Options

Name	Type	Default	Required	Description
callback	function	null	false	The function called when targets intersect/leaves the offset
offsett	number|string	0	false	The offset from top/left of viewport. A number indicates pixels from top/left of viewport. A string should be fx.: '50%'
enableLocationHash	boolean	false	false	Update the location hash when a target with an id intersects the offset
direction	string	'vertical'	false	The scroll direction

Methods

Name	Description
disconnect	Stop watching target(s)

Intersection Observer

Intersection Observer is the API used to determine if an element intersects the offset or not. Browser support is really good - With Safari adding support in 12.1, all major browsers now support Intersection Observers natively. Add the polyfill, so it doesn't break on older versions of iOS and IE11.

Polyfill

You can import the polyfill directly or use a service like polyfill.io to add it when needed.

yarn add intersection-observer

Then import it in your app:

import 'intersection-observer'