chartjs/Chart.js · error · Error

Cannot find a dataset at index ${datasetIndex}

Error message

Cannot find a dataset at index ${datasetIndex}

What it means

Tooltip.setActiveElements maps each {datasetIndex, index} to chart.getDatasetMeta(datasetIndex); like the controller's variant, getDatasetMeta returns undefined when the index is out of range or metasets are not yet built, and the tooltip throws. This is the tooltip's public programmatic API for forcing tooltip visibility on specific points.

Source

Thrown at src/plugins/plugin.tooltip.js:1112

	 * Get active elements in the tooltip
	 * @returns {Array} Array of elements that are active in the tooltip
	 */
  getActiveElements() {
    return this._active || [];
  }

  /**
	 * Set active elements in the tooltip
	 * @param {array} activeElements Array of active datasetIndex/index pairs.
	 * @param {object} eventPosition Synthetic event position used in positioning
	 */
  setActiveElements(activeElements, eventPosition) {
    const lastActive = this._active;
    const active = activeElements.map(({datasetIndex, index}) => {
      const meta = this.chart.getDatasetMeta(datasetIndex);

      if (!meta) {
        throw new Error('Cannot find a dataset at index ' + datasetIndex);
      }

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

    if (changed || positionChanged) {
      this._active = active;
      this._eventPosition = eventPosition;
      this._ignoreReplayEvents = true;
      this.update(true);
    }
  }

View on GitHub (pinned to cb02e1d207)

Solutions

1. Call setActiveElements only after chart.update()/render completes (metasets built).
2. Filter input against chart.data.datasets.length before calling.
3. Re-derive indices from the current data after any add/remove of datasets.
4. Use chart.getDatasetMeta(i) as a guard: include the entry only when it returns a truthy meta.

Example fix

// before
chart.tooltip.setActiveElements(
  [{ datasetIndex: 5, index: 1 }],
  { x: 10, y: 10 }
); // chart has 3 datasets -> throws

// after
const active = [{ datasetIndex: 5, index: 1 }].filter(
  ({ datasetIndex }) => datasetIndex >= 0 && datasetIndex < chart.data.datasets.length
);
if (active.length) chart.tooltip.setActiveElements(active, { x: 10, y: 10 });

// Clamp tooltip active elements to valid datasets before calling setActiveElements.
function safeTooltipActive(chart, activeElements, eventPosition) {
  const n = chart.data.datasets.length;
  const safe = activeElements.filter(
    ({ datasetIndex, index }) =>
      Number.isInteger(datasetIndex) && datasetIndex >= 0 && datasetIndex < n &&
      Number.isInteger(index) && index >= 0
  );
  if (safe.length) chart.tooltip.setActiveElements(safe, eventPosition);
  else chart.tooltip.setActiveElements([], eventPosition);
}

// Validate an active-element descriptor against the current dataset count.
function isValidTooltipActive(e, datasetCount) {
  return (
    e && typeof e.datasetIndex === 'number' && typeof e.index === 'number' &&
    e.datasetIndex >= 0 && e.datasetIndex < datasetCount && e.index >= 0
  );
}

When it happens

Trigger: Calling chart.tooltip.setActiveElements([{datasetIndex: 9, index: 0}], {x, y}) when the chart has fewer datasets; calling it before the first render built metasets; passing an index computed from a previous, larger dataset array after data was replaced.

Common situations: Programmatic tooltip display in tests or demos right after construction; syncing external selection UI to the chart after datasets were filtered; restoring tooltip state from a serialized snapshot whose indices no longer match.

Related errors

• No dataset found at index ${datasetIndex}
• Cannot determine type of '${id}' axis. Please provide 'axis'

AI-assisted analysis of chartjs/Chart.js@cb02e1d207 (2026-08-12). Data as JSON: /api/errors/95b62a0d905bbae2. Report an issue: GitHub.