svelte-scroller (demo)

A scroller component for Svelte apps.

Installation

yarn add @sveltejs/svelte-scroller

Usage

<script>
  import Scroller from "@sveltejs/svelte-scroller";

  let index, offset, progress;
</script>

<style>
  section {
    height: 80vh;
  }
</style>

<Scroller top="{0.2}" bottom="{0.8}" bind:index bind:offset bind:progress>
  <div slot="background">
    <p>
      This is the background content. It will stay fixed in place while the
      foreground scrolls over the top.
    </p>

    <p>Section {index + 1} is currently active.</p>
  </div>

  <div slot="foreground">
    <section>This is the first section.</section>
    <section>This is the second section.</section>
    <section>This is the third section.</section>
  </div>
</Scroller>

You must have one slot="background" element and one slot="foreground" element — see composing with <slot> for more info.

Parameters

The following parameters are available:

parameter	default	description
top	0	The vertical position that the top of the foreground must scroll past before the background becomes fixed, as a proportion of window height
bottom	1	The inverse of top — once the bottom of the foreground passes this point, the background becomes unfixed
threshold	0.5	Once a section crosses this point, it becomes 'active'
query	'section'	A CSS selector that describes the individual sections of your foreground
parallax	false	If true, the background will scroll such that the bottom edge reaches the bottom at the same time as the foreground. This effect can be unpleasant for people with high motion sensitivity, so use it advisedly

index, offset, progress and count

By binding to these properties, you can track the user's behaviour:

• index — the currently active section
• offset — how far the section has scrolled past the threshold, as a value between 0 and 1
• progress — how far the foreground has travelled, where 0 is the top of the foreground crossing top, and 1 is the bottom crossing bottom
• count — the number of sections

You can rename them with e.g. bind:index={i}.

Configuring webpack

If you're using webpack with svelte-loader, make sure that you add "svelte" to resolve.mainFields in your webpack config. This ensures that webpack imports the uncompiled component (src/index.html) rather than the compiled version (index.mjs) — this is more efficient.

If you're using Rollup with rollup-plugin-svelte, this will happen automatically.

License

LIL