tween

Simple, purely functional tweening function.

Installation

$ npm install @f/tween

Usage

var tween = require('@f/tween')
var applyStyles = require('@f/apply-styles')

function animate (element, start, end, duration, easing, cb) {
  var tick = tween(start, end)
  var t = 0

  requestAnimationFrame(function ticker () {
    var props = tick(t)
    applyStyles(element, props)

    if (props !== end) {
      t++
      requestAnimationFrame(ticker)
    } else {
      cb()
    }
  })
}

animate(element, {width: 10, left: 2}, {width: 100, left: 200})

API

tween(start, end, duration, easing, interval)

• start - Object containing the initial value of the properties you want to tween.
• end - Object containing the final value of the properties you want to tween.
• duration - The length of time, in milliseconds, your tween should be for. Defaults to 350ms.
• easing - An easing function that takes a tick value and interpolates it according to some easing function. Defaults to linear.
• interval - The tick length you want to use, in milliseconds. Defaults to 16.66ms (i.e. a single requestAnimationFrame timer).

Returns: A partially applied function that accepts a single parameter, t and returns the interpolated properties for that tick. The t parameter is a unitless value that corresponds to the frame of the tween you are requesting. So, if you are using requestAnimationFrame and the default interval, you just increment t once for each tick. t does not need to be an integer.

License

MIT