How to use the dygraphs/src-es5/dygraph.prototype function in dygraphs

},
      true /* no need to redraw */
    )
  }
}

function isValidPoint(p, opt_allowNaNY) {
  if (!p) return false // null or undefined object
  if (p.yval === null) return false // missing point
  if (p.x === null || p.x === undefined) return false
  if (p.y === null || p.y === undefined) return false
  if (isNaN(p.x) || (!opt_allowNaNY && isNaN(p.y))) return false
  return true
}

Dygraph.prototype.findClosestPoint = function(domX, domY) {
  if (Dygraph.VERSION !== '2.0.0') {
    console.error(
      `Dygraph version changed to ${Dygraph.VERSION} - re-copy findClosestPoint`
    )
  }
  var minXDist = Infinity
  var minYDist = Infinity
  var xdist, ydist, dx, dy, point, closestPoint, closestSeries, closestRow
  for (var setIdx = this.layout_.points.length - 1; setIdx >= 0; --setIdx) {
    var points = this.layout_.points[setIdx]
    for (var i = 0; i < points.length; ++i) {
      point = points[i]
      if (!isValidPoint(point)) continue

      dx = point.canvasx - domX
      dy = point.canvasy - domY