setActiveElements(activeElements) {
    const lastActive = this._active || [];
    const active = activeElements.map(({datasetIndex, index}) => {
      const meta = this.getDatasetMeta(datasetIndex);
      if (!meta) {
        throw new Error('No dataset found at index ' + datasetIndex);
      }

      return {
        datasetIndex,
        element: meta.data[index],
        index,
      };
    });
    const changed = !_elementsEqual(active, lastActive);

    if (changed) {
      this._active = active;
      // Make sure we don't use the previous mouse event to override the active elements in update.
      this._lastEvent = null;
      this._updateHoverStyles(active, lastActive);
    }
  }
Set active (hovered) elements
@param {array} activeElements New active data points