ScrollProgressObserver

Track the visibility and scroll progress of elements in the viewport. When do they enter and leave the viewport while scrolling? How far have they advanced through the viewport?

Demo

https://codesandbox.io/s/scrollprogressobserver-js-demo-xnm2k7?file=/src/Demo.js

Install

npm install '@superstructure.net/scrollprogressobserver'

Usage

import { ScrollProgressObserver } from "@superstructure.net/scrollprogressobserver";

const targetElement = document.querySelector(".target");
const options = {
  // This configuration starts tracking the target element when its
  // top edge passes a point 10vh from the viewport's bottom edge and
  // stops tracking when the target element's bottom edge passes a
  // point 20vh from the viewport's top edge.
  //
  // No worries, the default settings are fine, too.
  startTargetEdge: "start",
  endTargetEdge: "end",
  startViewportEdge: 0.9,
  endViewportEdge: 0.2,

  // Callbacks
  onEnter: () => {
    console.log("target element tracking started.");
  },
  onLeave: () => {
    console.log("target element tracking stopped.");
  },
  onProgress: (progress) => {
    console.log(
      `target element has progressed ${progress * 100}% through the viewport.`
    );
  },
};

const observer = new ScrollProgressObserver(targetElement, options);

Options

scrollDirection

y or x

Default: y

observeResize

Update the instance when the target element or the viewport is resized. Uses ResizeObserver internally.

Default: true

Manually call the resize() method when setting observeResize: false.

animationLoop

Default: true

Run an internal animation loop based on requestAnimationFrame. Manually call the onFrame method when using an external animation loop.

Tracking edges

startTargetEdge

Defines the target element's edge that starts tracking when scrolling in positive direction.

start, center, end or float from 0...1 (start...end).

Default: start

Example: When setting startTargetEdge: "start" with scrollDirection: "y", tracking starts when the target element's top edge passes the startViewportEdge (defaults to the bottom edge of the screen).

endTargetEdge

Defines the target element's edge that ends tracking when scrolling in positive direction.

start, center, end or float from 0...1 (start...end).

Default: end

Example: When setting endTargetEdge: "end" with scrollDirection: "y", tracking ends when the target element's bottom edge passes the endViewportEdge (defaults to the top edge of the screen).

startViewportEdge

Defines the viewport's edge that starts tracking when scrolling in positive direction.

start, center, end or float from 0...1 (start...end).

Default: end

Example: When setting startViewportEdge: "end" with scrollDirection: "y", tracking starts when the target element's startTargetEdge (defaults to the top edge of the target element) passes the bottom edge of the viewport .

endViewportEdge

Defines the viewport's edge that ends tracking when scrolling in positive direction.

start, center, end or float from 0...1 (start...end).

Default: start

Example: When setting endViewportEdge: "start" with scrollDirection: "y", tracking ends when the target element's endTargetEdge (defaults to the bottom edge of the target element) passes the top edge of the viewport .

Callbacks

onEnter and onLeave

Called when tracking of the target element starts/ends. Can be controlled via startTargetEdge, endTargetEdge, startViewportEdge and endViewportEdge. Receives the target element as first argument.

onEnterViewport and onLeaveViewport

Called when the target element enters/leaves the viewport. Ignores startTargetEdge, endTargetEdge, startViewportEdge and endViewportEdge. Receives the target element as first argument.

onProgress

Called every frame whil tracking of the target element is active. Receives progress in the range 0...1 as first argument and the target element as the second argument.