Sonar.js

A tiny library for detecting when a browser is scrolled to the bottom of a web page.

You could use this, for example, on a blog to show a popover when a reader has finished a post, letting them know they can receive new posts by email if they submit their email address.

Installation

yarn add sonar-js

The package comes in three formats: CommonJS, Universal Module Definition, and ECMAScript Module.

Format	package.json key	Path
CJS	main	dist/sonar.js
UMD	umd:main	dist/sonar.umd.js
ESM	module	dist/sonar.m.js

The package is built on-the-fly before publishing to NPM so the dist folder is not in the repo. Use the links above to get the built files.

Usage

Create an instance of Sonar passing in the window and then call ping passing in the range to the bottom of the page, a function to call when within range of the bottom and an optional function to call when not within range of the bottom.

When ping is called one of the callbacks will fire, depending on whether or not the scroll is currently within range of the page bottom. The behavior after that depends on which callbacks are provided.

One callback

var sonar = new Sonar(window)

var withinRangeOfPageBottom = function() {
  document.querySelector('.popover').classList.remove('hidden')
}

sonar.ping(600, withinRangeOfPageBottom)

Without a second callback to fire when losing the bottom of the page this is essentially a one-time use. The callback will fire once when finding the bottom of the page and then never fire again, even if you scroll up and back down again.

This is useful for making a permanent change when someone scrolls to the bottom of the page.

Two callbacks

var sonar = new Sonar(window)

var withinRangeOfPageBottom = function() {
  document.querySelector('.popover').classList.remove('hidden')
}

var notWithinRangeOfPageBottom = function() {
  document.querySelector('.popover').classList.add('hidden')
}

sonar.ping(600, withinRangeOfPageBottom, notWithinRangeOfPageBottom)

With a second callback to fire when losing the bottom of the page this becomes a toggle. The callbacks will only fire once when finding the bottom or losing the bottom. That is, the callbacks will only fire or re-fire when the state changes.

This is useful for making a temporary change when someone scrolls to the bottom of the page and then reversing it when they scroll away from the bottom of the page.

Tests

yarn test

Contributing

1. Fork it ( https://github.com/brandonweiss/sonar-js/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am "Add some feature")
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request