typeAheadDown() {
      for (
        let i = this.typeAheadPointer + 1;
        i < this.filteredOptions.length;
        i++
      ) {
        if (this.selectable(this.filteredOptions[i])) {
          this.typeAheadPointer = i
          break
        }
      }
    }
Move the typeAheadPointer visually down the list by
setting it to the next selectable option.
@return {void}