downup

Tiny listener on numerical value changes. Works in Node and with Browserify.

Install

With npm do:

$ npm install downup --save

Usage

Basic examples

var Downup = require('downup');
 
// Create instance
var downup = new Downup();
 
// Add listener
downup.on(1, function(offset) {
  console.log('Reached 1 and going %s', offset > 0 ? 'up' : 'down');
});
 
// Will trigger since default value is 0
downup.update(2);
 
// Will trigger again with offset -1
downup.update(0);
 
// Will not trigger
downup.set(2);
 
// Remove all listeners attached to number 1
downup.off(1);
 
// Will not trigger since the listener has been removed
downup.update(0);

Sticky example

// Update on scroll (please debounce this ;)
window.addEventListener('scroll', function(e){
  downup.update(window.scrollY);
});
 
// Listen to menu and add sticky class
var menu = document.querySelector('#menu');
 
downup.on(menu.offsetTop, function(diff){ 
  menu.classList[diff > 0 ? 'add' : 'remove']('stick');
});
 

Instance Methods

downup extends TinyEmitter and inherit from its instance methods.

on(number, callback[, context])

Subscribe to a number

• number - the number to subscribe to
• callback - the function to call when number is reached
• context - (OPTIONAL) - the context to bind the event callback to

once(number, callback[, context])

Subscribe to an event only once

• number - the number to subscribe to
• callback - the function to call when number is reached
• context - (OPTIONAL) - the context to bind the event callback to

off(number[, callback])

Unsubscribe from an number. If no callback is provided, it unsubscribes you from all callbacks registered to this number.

• number - the number to unsubscribe from
• callback - the function used when binding to the number

update(number)

Update downup.value and trigger any registered numbers between old value and this one

• number - the new value

set(number)

Similar to update(number) but it will not trigger any event.

• number - the new value

emit(number[, offset])

Trigger a specific number (should not be used...)

• number - the number to emit
• offset - the offset to pass to the callbacks

Test and Build

Build (Tests, Browserifies, and minifies)

npm install
npm run build

Test

npm install
npm test

License

MIT