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Detect Scroll 📜️ 🔍️ 👀️

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

Coverage:statements Coverage:functions Coverage:lines License: MIT

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.

Note: Open your console to preview debug mode


Installation

npm install @egstad/detect-scroll

Usage

Example One

  1. Install and import detectScroll.
  2. 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.
  3. Register the Event listeners that you'd like to use. Any events that are not explicitly defined will not fire.
  4. 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,
  },
})

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