changeSelectionByScroll(scrollPos) {
      const newlySelectedIndex = this.getClosestStepIndexByScrollPos(scrollPos);
      const stepToSelect = this.slottedSteps[newlySelectedIndex];
      // Skip if already selected - stop.
      if (this.selectedStepIndex === newlySelectedIndex) {
        return;
      }
      // If the calculated index is in range,
      // change selection and fire "step-change".
      if (!stepToSelect.disabled && newlySelectedIndex >= 0 && newlySelectedIndex <= this.stepsCount - 1) {
        this.switchSelectionFromOldToNewStep(this.selectedStep, stepToSelect, newlySelectedIndex, false);
        this.selectionRequestedByScroll = true;
      }
    }
Called upon <code>onScroll</code>.
Selects the closest step, based on the user scroll position.
@param {Integer} scrollPos the current scroll position
@private