Waypoint DOM removal detection

context.js

  ...
  /* Public */
  /* http://imakewebthings.com/waypoints/api/context-refresh */
  Context.prototype.refresh = function() {
    /*eslint-disable eqeqeq */
    var isWindow = this.element == this.element.window
    /*eslint-enable eqeqeq */
    var contextOffset = isWindow ? undefined : this.adapter.offset()
    var triggeredGroups = {}
    var axes

    this.handleScroll()
    axes = {
      horizontal: {
        contextOffset: isWindow ? 0 : contextOffset.left,
        contextScroll: isWindow ? 0 : this.oldScroll.x,
        contextDimension: this.innerWidth(),
        oldScroll: this.oldScroll.x,
        forward: 'right',
        backward: 'left',
        offsetProp: 'left'
      },
      vertical: {
        contextOffset: isWindow ? 0 : contextOffset.top,
        contextScroll: isWindow ? 0 : this.oldScroll.y,
        contextDimension: this.innerHeight(),
        oldScroll: this.oldScroll.y,
        forward: 'down',
        backward: 'up',
        offsetProp: 'top'
      }
    }

    for (var axisKey in axes) {
      var axis = axes[axisKey]
      for (var waypointKey in this.waypoints[axisKey]) {
        var waypoint = this.waypoints[axisKey][waypointKey]
        var adjustment = waypoint.options.offset
        var oldTriggerPoint = waypoint.triggerPoint
        var elementOffset = 0
        var freshWaypoint = oldTriggerPoint == null
        var contextModifier, wasBeforeScroll, nowAfterScroll
        var triggeredBackward, triggeredForward
        
        if (waypoint.element.parentNode === null) {
          delete(this.waypoints[axisKey]);
          continue;
        }

        if (waypoint.element !== waypoint.element.window) {
          elementOffset = waypoint.adapter.offset()[axis.offsetProp]
        }

        if (typeof adjustment === 'function') {
          adjustment = adjustment.apply(waypoint)
        }
        else if (typeof adjustment === 'string') {
          adjustment = parseFloat(adjustment)
          if (waypoint.options.offset.indexOf('%') > - 1) {
            adjustment = Math.ceil(axis.contextDimension * adjustment / 100)
          }
        }

        contextModifier = axis.contextScroll - axis.contextOffset
        waypoint.triggerPoint = Math.floor(elementOffset + contextModifier - adjustment)
        wasBeforeScroll = oldTriggerPoint < axis.oldScroll
        nowAfterScroll = waypoint.triggerPoint >= axis.oldScroll
        triggeredBackward = wasBeforeScroll && nowAfterScroll
        triggeredForward = !wasBeforeScroll && !nowAfterScroll

        if (!freshWaypoint && triggeredBackward) {
          waypoint.queueTrigger(axis.backward)
          triggeredGroups[waypoint.group.id] = waypoint.group
        }
        else if (!freshWaypoint && triggeredForward) {
          waypoint.queueTrigger(axis.forward)
          triggeredGroups[waypoint.group.id] = waypoint.group
        }
        else if (freshWaypoint && axis.oldScroll >= waypoint.triggerPoint) {
          waypoint.queueTrigger(axis.forward)
          triggeredGroups[waypoint.group.id] = waypoint.group
        }
      }
    }

    Waypoint.requestAnimationFrame(function() {
      for (var groupKey in triggeredGroups) {
        triggeredGroups[groupKey].flushTriggers()
      }
    })

    return this
  }
  ...