mobile-pull-to-refresh/src/ontouchpan.js

Pull to refresh

export default function({ element, onpanstart, onpanmove, onpanend }) {
  let touchId, startX, startY, panstartCalled

  function calcMovement(e) {
    const touch = Array.prototype.slice.call(e.changedTouches).filter(touch => touch.identifier === touchId)[0]
    if (!touch) return false

    e.deltaX = touch.screenX - startX
    e.deltaY = touch.screenY - startY
    return true
  }

  function touchstart(e) {
    const touch = e.changedTouches[0]
    touchId = touch.identifier
    startX = touch.screenX
    startY = touch.screenY
  }

  function touchmove(e) {
    if (calcMovement(e)) {
      if (onpanstart && !panstartCalled) {
        onpanstart(e)
        panstartCalled = true
      }

      onpanmove(e)
    }
  }

  function touchend(e) {
    if (calcMovement(e)) onpanend(e)
  }

  element.addEventListener('touchstart', touchstart)
  if (onpanmove) element.addEventListener('touchmove', touchmove)
  if (onpanend) element.addEventListener('touchend', touchend)

  return function() {
    element.removeEventListener('touchstart', touchstart)
    if (onpanmove) element.removeEventListener('touchmove', touchmove)
    if (onpanend) element.removeEventListener('touchend', touchend)
  }
}