Detect Scroll 📜️ 🔍️ 👀️

A performant and lightweight (~1.6kb) ES6 module for detecting scroll activity (direction + location) for X and/or Y axis

Introduction

The default scroll event listener is amazing and all, but isn't exactly the most usable tool out of the box. It's all, "Hey look, a user scrolled!". And I'm like "Great! But like, in what direction and where did they stop?". And then it's all like, "IDFK, how about you do some math and figure it out".

In short, this little library adds a handful of helpful CustomEvent's which make scroll detection a little more insightful.

View Example

Note: Open your console to preview debug mode

Installation

npm install @egstad/detect-scroll

Usage

Example One

Install and import detectScroll.
Select an individual element you'd like to monitor the scroll activity of. Can be a string selector (ie: '.scroll-container'), or any valid HTMLElement. In our case, we'll use the window.
Register the Event listeners that you'd like to use. Any events that are not explicitly defined will not fire.
If/when you want to destroy the instance, running destroy() will remove all event listeners.

import detectScroll from '@egstad/detect-scroll'

// setup instance & events
const instance = new detectScroll(window, {
  events: {
    scrollUp: foo(),
    scrollDown: bar(),
  },
})

// if/when you want to destroy the instance and events
instance.destroy()

Example Two

Another way to get up and running with this library is to handle the events yourself. This option registers and dispatches all Events, but you'll have to add/remove the event listeners yourself.

import detectScroll from '@egstad/detect-scroll'

// setup instance
const instance = new detectScroll(window)

// setup events
window.addEventListener('scrollUp', foo)
window.addEventListener('scrollDown', bar)

// if/when you want to destroy all events
window.removeEventListener('scrollUp', foo)
window.removeEventListener('scrollDown', bar)

Default Configuration

const instance = new detectScroll(window, {
  vertical: true,
  horizontal: true,
  passiveMode: true,
  debugMode: false,
  events: undefined,
})

Properties & Events worth knowing about

Optional Properties

Optional Properties	Default Value	Description
`vertical`	`true`	Registers & Dispatches y-axis activity
`horizontal`	`true`	Registers & Dispatches x-axis activity
`passiveMode`	`true`	Determines if scroll event is passive or not
`debugMode`	`false`	Logs events in console as they dispatch
`events`	`undefined`	Event overrides (see Events section for more)

Events

Scroll events are dispatched using CustomEvent's. Here's a gorgeous list of all 10.

If you would like to a specific selection of them, check out this example.

Custom Event Name	Description
`scrollStart`	Fired when scrolling begins
`scrollStop`	Fired when scrolling ends
`scrollX`	Fired every time x position updates
`scrollY`	Fired every time y position updates
`scrollUp`	Fired when scrolling up
`scrollDown`	Fired when scrolling down
`scrollLeft`	Fired when scrolling left
`scrollRight`	Fired when scrolling right
`scrollMinX`	Fired when the left-most part of el/window is reached
`scrollMaxX`	Fired when the right-most part of el/window is reached
`scrollMinY`	Fired when top of element/window is reached
`scrollMaxY`	Fired when bottom of element/window is reached

Event Template

const foo = (ev) => {
  console.log(ev.type)
}

const instance = new detectScroll(window, {
  events: {
    // exclude any of these and the event's won't be registered or fired
    scrollStart: foo,
    scrollStop: foo,
    scrollX: foo,
    scrollY: foo,
    scrollUp: foo,
    scrollDown: foo,
    scrollLeft: foo,
    scrollRight: foo,
    scrollMinX: foo,
    scrollMaxX: foo,
    scrollMinY: foo,
    scrollMaxY: foo,
  },
})

egstad-construct / detect-scroll