Scrollytelling with IntersectionObserver.
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README.md

scrollama.js

scrollama.js

Scrollama is a modern & lightweight JavaScript library for scrollytelling using IntersectionObserver in favor of scroll events.

Notes: As of version 1.4.0, you must manually add the IntersectionObserver polyfill for cross-browser support. See installation for details. Although it remains in the API (for now), it is recommended to use the CSS property position: sticky; instead of .onContainerEnter and .onContainerExit. Full blog post here.

As seen on The Pudding:

Jump to examples.

Why?

Scrollytelling can be complicated to implement and difficult to make performant. The goal of this library is to provide a simple interface for creating scroll-driven interactives. Scrollama is focused on performance by using IntersectionObserver to handle element position detection. It offers an opinionated (but popular) scrollytelling pattern to reduce more involved DOM calculations. The sticky graphic pattern (enter-stick-exit) can be seen below. Check out my blog post for a deeper introduction.

scrollytelling pattern

Examples

Note: most of these demos use D3 to keep the code concise, but this can be used with any library, or with no library at all.

Installation

Note: As of version 1.4.0, the IntersectionObserver polyfill has been removed from the build. You must include it yourself for cross-browser support.

Old school (exposes the scrollama global):

<script src='https://unpkg.com/intersection-observer@0.5.0/intersection-observer.js'></script>
<script src='https://unpkg.com/scrollama'></script>

New school:

npm install scrollama intersection-observer

And then import/require it:

import 'intersection-observer';
import scrollama from 'scrollama'; // or...
const scrollama = require('scrollama');

How to use

Basic

You can use this library to simply trigger steps, similar to something like Waypoints. This is useful if you need more control over your interactive, or you don't want to follow the sticky scrollytelling pattern.

You can use any id/class naming conventions you want. The HTML structure should look like:

<!--you don't need the "data-step" attr, but can be useful for storing instructions for JS -->
<div class='step' data-step='a'></div>
<div class='step' data-step='b'></div>
<div class='step' data-step='c'></div>
// instantiate the scrollama
const scroller = scrollama();

// setup the instance, pass callback functions
scroller
  .setup({
    step: '.step' // required - class name of trigger steps
  })
  .onStepEnter(handleStepEnter)
  .onStepExit(handleStepExit);

Sticky Graphic

Update: I recommend using the CSS property position:sticky;. You can simply use the triggers like above, and let the CSS handle everything else. Full blog post here.

To implement the sticky graphic scrollytelling pattern, you need the following three elements (container, graphic, steps). The structure should look like:

<!-- container = ".scroll" -->
<div class='scroll'>
  <!-- graphic = ".scroll__graphic" -->
  <div class='scroll__graphic'>
    <!--graphic / chart code here-->
  </div>
  <div class='scroll__text'>
    <!-- steps = ".step" -->
    <div class='step' data-step='a'></div>
    <div class='step' data-step='b'></div>
    <div class='step' data-step='c'></div>
  </div>
</div>
// instantiate the scrollama
const scroller = scrollama();

// setup the instance, pass callback functions
scroller
  .setup({
    step: '.scroll__text .step', // required
    container: '.scroll', // required (for sticky)
    graphic: '.scroll__graphic' // required (for sticky)
  })
  .onStepEnter(handleStepEnter)
  .onStepExit(handleStepExit)
  .onContainerEnter(handleContainerEnter)
  .onContainerExit(handleContainerExit);

API

scrollama.setup([options])

options:

  • step (string): Selector (or array of elements) for the step elements that will trigger changes. required
  • container (string): Selector (or element) for the element that contains everything for the scroller. optional
  • graphic (string): Selector (or element) for the graphic element that will become fixed. optional
  • offset (number, 0 - 1): How far from the top of the viewport to trigger a step. (default: 0.5)
  • progress (boolean): Whether to fire incremental step progress updates or not. (default: false)
  • threshold (number, 1+): The granularity of the progress interval, in pixels (smaller = more granular updates). (default: 4)
  • order (boolean): Whether to preserve step triggering order if they fire out of sync (eg. ensure step 2 enters after 1 exits). (default: true)
  • once (boolean): Only trigger the step to enter once then remove listener. default: false
  • debug (boolean): Whether to show visual debugging tools or not. (default: false)

scrollama.onStepEnter(callback)

Callback that fires when the top or bottom edge of a step element enters the offset threshold.

The argument of the callback is an object: { element: DOMElement, index: number, direction: string }

element: The step element that triggered

index: The index of the step of all steps

direction: 'up' or 'down'

scrollama.onStepExit(callback)

Callback that fires when the top or bottom edge of a step element exits the offset threshold.

The argument of the callback is an object: { element: DOMElement, index: number, direction: string }

element: The step element that triggered

index: The index of the step of all steps

direction: 'up' or 'down'

scrollama.onStepProgress(callback)

Callback that fires the progress (0 - 1) a step has made through the threshold.

The argument of the callback is an object: { element: DOMElement, index: number, progress: number }

element: The step element that triggered

index: The index of the step of all steps

progress: The percent of completion of the step (0 - 1)

scrollama.onContainerEnter(callback)

Callback that fires when the top of container becomes flush with viewport or the graphic becomes fully in view coming from the bottom of the container.

The argument of the callback is an object: { direction: string }

direction: 'up' or 'down'

scrollama.onContainerExit(callback)

Callback that fires when the top of container goes below viewport or the graphic becomes not full in view leaving the bottom of the container.

The argument of the callback is an object: { direction: string }

direction: 'up' or 'down'

scrollama.offsetTrigger([number])

Get or set the offset percentage. Value must be between 0-1.

scrollama.resize()

Tell scrollama to get latest dimensions the browser/DOM. It is best practice to throttle resize in your code, update the DOM elements, then call this function at the end.

scrollama.enable()

Tell scrollama to resume observing for trigger changes. Only necessary to call if you have previously disabled.

scrollama.disable()

Tell scrollama to stop observing for trigger changes.

scrollama.destroy()

Removes all observers and callback functions.

Tips

  • Always call scrollama.resize() after a window resize event to ensure scroll triggers update with new dimensions.
  • Avoid using viewport height (vh) in your CSS because scrolling up and down constantly triggers vh to change, which will also trigger a window resize.

Known Issues

The .onStepProgress function does not perform desirably in Safari, returning infrequent updates.

Alternatives

Logo

Logo by the awesome Elaina Natario

License

MIT License

Copyright (c) 2017 Russell Goldenberg

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.