Scroll-watcher NPM

scroll-watcher

A lightweight, blazing fast, rAF based, scroll watcher.

A more up-to-date approach to this scrolling watchers stuff. Slightly inspired by scrollMonitor.

Demos

How to use it?

→ CDN Hosted - jsDelivr

<script src="https://cdn.jsdelivr.net/npm/scroll-watcher@latest/dist/scroll-watcher.min.js"></script>

→ Self hosted

Download latest release.

→ NPM

npm install scroll-watcher

Instantiate and watch for a specific (or a list) DOM element

var scroll = new ScrollWatcher();
scroll
  .watch("my-element")
  .on("enter", function(evt) {
    console.log("I'm partially inside viewport");
  })
  .on("enter:full", function(evt) {
    console.log("I'm entirely within the viewport");
  })
  .on("exit:partial", function(evt) {
    console.log("I'm partially out of viewport");
  })
  .on("exit", function(evt) {
    console.log("I'm out of viewport");
  });

Make some decision when page is loaded (or reloaded)

watcher.on("page:load", function(evt) {
  // maybe trigger a scroll?
  window.setTimeout(() => window.scrollBy(0, 1), 20);
});

Instance Methods

watch(target, offset)

target - {String|Element} String or DOM node.
offset - {Number|Object|undefined} (optional) Element offset.

Returns:

Methods
- on/once/off - common events
- update - updates the location of the element in relation to the document
Properties
- target - DOM node being watched

windowAtBottom(offset)

offset - {Number|undefined} (optional) How far to offset.

windowAtTop(offset)

offset - {Number|undefined} (optional) How far to offset.

Instance Events - `on/once/off`

You can simply watch for scrolling action:

var watcher = new ScrollWatcher();
watcher.on("scrolling", function(evt) {
  console.log(evt);
});

// or just once
watcher.once("scrolling", function(evt) {
  console.log(evt);
});

// and turn it off (later)
watcher.off("scrolling");