controller.js

this.set('selectedItems', []) // TODO prefix
    this.set('previousRangeEndItemIndex', null) // TODO prefix
    this.set('rangeAnchorIndex', null) // TODO prefix

    this.set('actions.select', function ({isCheckboxSelect, isRangeSelect, isCurrentlySelected, isSpecificSelect, item}) {
      const selectedItems = this.get('selectedItems')

      // Selects are proccessed in order of precedence: checkbox, specific, range, default
      if (isCheckboxSelect) {
        // Checkbox select works like a specific select, the target item
        // is selected/deselected without modifying other existing selections
        const isSelected = !isCurrentlySelected
        this.setProperties({
          rangeAnchorItem: isSelected ? item : null,
          previousRangeEndItemIndex: null
        })

        if (isSelected) {
          selectedItems.pushObject(item)
        } else {
          selectedItems.removeObject(item)
        }
      } else if (isSpecificSelect) {
        // Select/deselect the item without modifying other existing selections
        const isSelected = !isCurrentlySelected
        this.setProperties({
          rangeAnchorItem: isSelected ? item : null,
          previousRangeEndItemIndex: null
        })

        if (isSelected) {
          selectedItems.pushObject(item)
        } else {
          selectedItems.removeObject(item)
        }
      } else if (isRangeSelect) {
        // The range anchor is the previous selection if:
        // - the selection was positive
        // - the selection wasn't the end of a range select
        const rangeAnchorItem = this.get('rangeAnchorItem')
        if (isNone(rangeAnchorItem)) {
          // A range select without an established anchor is a specific select;
          // however, a range select will always issue a positive select
          this.setProperties({
            rangeAnchorItem: item,
            previousRangeEndItemIndex: null
          })
          selectedItems.pushObject(item)
        } else {
          // Select all of the items between the anchor and the item (inclusive)
          // The range anchor doesn't update when selecting the end of a range
          const items = this.get('items')
          const rangeAnchorIndex = items.indexOf(rangeAnchorItem)
          const itemIndex = items.indexOf(item)
          const isSelectionAscending = rangeAnchorIndex < itemIndex
          const rangeStartIndex = isSelectionAscending ? rangeAnchorIndex : itemIndex
          const rangeEndIndex = isSelectionAscending ? itemIndex : rangeAnchorIndex

          // If a previous range end was selected, deselect all selections no longer in the range
          const previousRangeEndItemIndex = this.get('previousRangeEndItemIndex')
          let deselectedItems = []
          if (!isNone(previousRangeEndItemIndex)) {
            const isPreviousSelectionAscending = rangeAnchorIndex < previousRangeEndItemIndex
            if (isSelectionAscending === isPreviousSelectionAscending) {
              if (isSelectionAscending && itemIndex < previousRangeEndItemIndex) {
                deselectedItems = items.slice(itemIndex + 1, previousRangeEndItemIndex + 1)
              } else if (!isSelectionAscending && itemIndex > previousRangeEndItemIndex) {
                deselectedItems = items.slice(previousRangeEndItemIndex, itemIndex)
              }
            } else if (isPreviousSelectionAscending) {
              deselectedItems = items.slice(rangeAnchorIndex + 1, previousRangeEndItemIndex + 1)
            } else {
              deselectedItems = items.slice(previousRangeEndItemIndex, rangeAnchorIndex)
            }
          }

          // Set the (now) previous range end item index
          this.set('previousRangeEndItemIndex', itemIndex)

          selectedItems.pushObjects(items.slice(rangeStartIndex, rangeEndIndex + 1))
          selectedItems.removeObjects(deselectedItems)
        }
      } else {
        // If the item is part of a previous set of selections
        // the item remains selected while the rest are deselected
        const isInPreviousSelections =
          selectedItems.get('length') > 1 &&
          selectedItems.findBy('id', item.get('id'))

        const isSelected = isInPreviousSelections ? true : !isCurrentlySelected
        this.setProperties({
          rangeAnchorItem: isSelected ? item : null,
          previousRangeEndItemIndex: null
        })

        // Default select clears out any prior selections
        if (isSelected) {
          selectedItems.setObjects([item])
        } else {
          selectedItems.clear()
        }
      }
    })

frost-list-item.hbs

click (event) {
    // Acceptable event modifiers for range selection
    const simpleClick = Ember.ViewUtils.isSimpleClick(event)
    const specificSelectModifier = (new window.UAParser()).getOS() === 'Mac OS' ? event.ctrlKey : event.metaKey // TODO Move instance to a service
    const rangeSelectModifier = event.shiftKey

    // Only process simple clicks or clicks with the acceptable modifiers
    if (simpleClick || specificSelectModifier || rangeSelectModifier) {
      event.preventDefault()
      event.stopPropagation()

      this.onSelect({
        isCheckboxSelect: $(event.target).hasClass('frost-list-selection-indicator'),
        isRangeSelect: rangeSelectModifier,
        isCurrentlySelected: this.get('model.isSelected'),
        isSpecificSelect: specificSelectModifier,
        item: this.get('model')
      })
    }
  }