react-date-picker/src/utils/isInRange.js

A carefully crafted date picker for React

export default (moment, configOrRange) => {

  let range = configOrRange
  let inclusive = true

  if (!Array.isArray(configOrRange) && typeof configOrRange == 'object'){
    range = configOrRange.range

    if (configOrRange.inclusive !== undefined){
      inclusive = !!configOrRange.inclusive
    }
  }

  const start = range[0]
  const end = range.length >= 2 && range[range.length - 1]

  if (!moment){
    return false
  }

  if (start && end){
    const insideRange = start.isBefore(moment) && end.isAfter(moment)

    return inclusive?
      insideRange || start.isSame(moment) || end.isSame(moment):
      insideRange
  }

  return false
}