tweezer-

tweezer-demo-1.es6

document.querySelector('#animate-height-button')
.onclick = () => {
  if (!isRunning) {
    new Tweezer({
      start: animatedHeight.getBoundingClientRect().height,
      end: grow(shouldGrow)
    })
    .on('tick', v=> animatedHeight.style.height = v +'px')
    .on('done', ()=> {
      shouldGrow = !shouldGrow
      isRunning = false
    })
    .begin()
    isRunning = true
  }
}