sonar-js

Sonar.js

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

For example, you might use this 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 two types of modules: UMD and ES6.

• Universal Module Definition — ES5 wrapped in a UMD module; suitable for simpler build systems or even just dropping it directly onto a page. No transpiling necessary. Your build system can find it via the main key in package.json or in dist/sonar.js.
• ES6 Module — ES5 wrapped in an ES6 module; suitable for build systems that know how to handle ES6 modules. The code itself has already been transpiled to ES5 for convenience, but a build system will still have to transpile the module declaration as no browsers currently support ES6 modules. Your build system can find it via the module or jsnext:main keys in package.json or in dist/sonar.es.js.

The package is built on-the-fly before publishing to NPM so the dist folder is not in the repo. If you’d like the built files install it via yarn or npm and pluck the file you need out of node_modules/sonar-js/dist/.

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, persistent 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 permanent, 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