multiple selection array, inspired on selection of gmail list of emails

multipleSelect.js

// Reusable function to select multimple itens
// with start and end element
// array: array of elements to select
// selection: previously selected elements
// start: first element selected
// end: last element selected

function multipleSelect(array, selection, start, end) {
  const startIndex = array.findIndex(item => item == start)
  const endIndex = array.findIndex(item => item == end)
  const min = startIndex < endIndex 
  	? selection.includes(start) ? startIndex + 1 : startIndex
    : endIndex
  const max = (startIndex > endIndex ? startIndex : endIndex) + 1
  const currentSelection = array.slice(min, max)
  
  const selectedItems = () => {
    const itemsToAdd = currentSelection.filter(e => (
      !selection.includes(e)
    ))
    const itemsToRemove = currentSelection.filter(e => (
      selection.includes(e)
    ))
    
    if (itemsToAdd.length > itemsToRemove.length) {
      return [...selection, ...itemsToAdd]
    } else {
      return selection.filter(e => (
        !itemsToRemove.includes(e)
      ))
    }
  }

  return selectedItems()
}