DateFNS closestIndexTo returns NaN

I need to get the closest date from an array of dates with DateFNS v.2.0.1 closestIndexTo. I'm currently getting NaN returned. What am I missing here?

(val = 2019-09-01) 
(arrDates = 2019-09-01,2019-09-03,2019-09-03,2019-09-04,2019-09-05,2019-09-05,2019-09-23,2019-10-01,2019-11-18)

getClosestToDate(val,arr) {
  var arrDates = [_.map(arr, 'date')]
  var closestDate = closestIndexTo(parseISO(val), arrDates)
  return closestDate
},

from DateFNS closestIndexTo returns NaN