A little extension class of of the Handsontable DateEditor that makes sure the datepicker opens to the top if needed. (Needs modifications for other directions) See https://github.com/handsontable/handsontable/issues/3483

handsontable-datepicker-helper.ts

const Base = (Handsontable.editors.DateEditor as any).prototype as any
const DateEditorHelper = Base.extend()
DateEditorHelper.prototype.showDatepicker = function(...args: any[]) {
  Base.showDatepicker.apply(this, ...args)
  const offset = (this.TD as HTMLElement).getBoundingClientRect()
  const picker = this.$datePicker.el as HTMLElement
  const pickerRect = picker.getBoundingClientRect()
  if (
    (this.cellProperties &&
    this.cellProperties.datePickerConfig &&
    this.cellProperties.datePickerConfig.position &&
    this.cellProperties.datePickerConfig.position.indexOf("top") !== -1)
    ||
    offset.top >= window.innerHeight - pickerRect.height
  ) {
    this.datePickerStyle.top = (window.pageXOffset + offset.top - pickerRect.height) + "px"
  }
}

line 14 should be:

offset.bottom >= window.innerHeight - pickerRect.height

no?

because if you don't have the picker anchored to the top (which you are already checking for) then it is gonna be anchored on the bottom and has an additional offset the height of the TD element