Package Exports

react-scroll-agent

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Readme

React Scroll Agent

Tiny, 6 KB (pre-gzip) scrollspy component that performantly runs at 60 FPS thanks to requestAnimationFrame and @reach/observe-rect.

react-scroll-agent example

Install

npm i --save react-scroll-agent @reach/observe-rect

Example

import ScrollAgent from 'react-scroll-agent';

<ScrollAgent
  nav={({ current, positions }) => (
    <menu>
      <a href="#section-1" className={current === 0 ? 'is-active' : ''}>Section 1</a>
      <a href="#section-2" className={current === 1 ? 'is-active' : ''}>Section 2</a>
      <a onClick={() => window.scrollTo(0, positions[2])} className={current === 1 ? 'is-active' : ''}>
        Section 3
      </a>
    </menu>
  )}
  selector="section[data-scrollspy]"
  threshold="center"
>
  <section id="section-1" data-scrollspy>
    <h1>Section 1</h1>
  </section>
  <section id="section-2" data-scrollspy>
    <h1>Section 2</h1>
  </section>
  <section id="section-3" data-scrollspy>
    <h1>Section 3</h1>
  </section>
</ScrollAgent>

Props

Name	Type	Required	Default	Description
`selector`	`String`	✅		Any CSS selector to specify which elements in `children` to attach the scrollspy to.
`children`	React Node			Standard child passthrough. This is where it watches for scroll events.
`detectEnd`	`Boolean`		`true`	If `true`, the last index will be highlighted when scrolled to the bottom. If `false`, then when scrolled to the bottom, `current` will return whichever container is currently at `threshold`.
`nav`	React Node			Render prop that returns `current` index in view and all `positions` of items.
`threshold`	`String`		`"top"`	Trigger point at which `current` watches. Accepts `"top"`, `"center"`, or `"bottom"` (if a specific threshold is needed, simply add `padding` to the top or bottom of a container).

Nav

The nav render prop returns the following items:

<ScrollAgent
  nav={({ current, positions }) => (
    <menu>
      <a href="#section-1" className={current === 0 ? 'is-active' : ''}>Section 1</a>
      <a
        href="#"
        onClick={e => {
          e.preventDefault();
          window.scrollTo(0, positions[1]);
        }}
        className={current === 1 ? 'is-active' : ''}
      >
        Section 2
      </a>
    </menu>
  )}

Name	Type	Description
`current`	`Number`	The index of the current item in view, in visual descending order on the page (may not necessarily be DOM order).
`positions`	`[Number]`	An array of all absolute Y values on the page, ordered from top to bottom. Useful for animating scroll to a certain item.

Notes

If the first item isn’t in view, then current will return -1. This is expected, and allows more flexibility in styling. If you always want the first item to be highlighted, then check that current === 0 || current === -1.
This component achieves performance by letting you handle all animations. If you need smooth scrolling from your nav, you can easily add another library to handle that using positions.
requestAnimationFrame won’t fire more than 60FPS, so it’s a perfect native debouncing function for managing scroll events and reflows.
This component won’t update current or positions unless it actually changes, preventing unnecessary re-renders in React.