react-virtualized/playground/tests.js

React components for efficiently rendering large, scrollable lists and tabular data

function createScrollingTestCase (component) {
  var scrollDown = getUrlParam('direction') !== 'up'

  return function testCase (completedCallback) {
    component.scrollTop = scrollDown
      ? 0
      : component.scrollHeight

    var maxScrollTop = component.scrollHeight

    var interval = 1
    var scrollTop = component.scrollTop

    function incrementScrollDown () {
      if (!testRunner.isRunning()) {
        return
      }

      interval *= 1.05
      scrollTop = Math.min(scrollTop + interval, maxScrollTop)

      component.scrollTop = scrollTop

      if (scrollTop < maxScrollTop) {
        requestAnimationFrame(incrementScrollDown)
      } else {
        completedCallback()
      }
    }

    function incrementScrollUp () {
      if (!testRunner.isRunning()) {
        return
      }

      interval *= 1.05
      scrollTop = Math.max(scrollTop - interval, 0)

      component.scrollTop = scrollTop

      if (scrollTop > 0) {
        requestAnimationFrame(incrementScrollUp)
      } else {
        completedCallback()
      }
    }

    if (scrollDown) {
      incrementScrollDown()
    } else {
      incrementScrollUp()
    }
  }
}