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# Legend Configuration
The chart legend displays data about the datasets that area appearing on the chart.
## Configuration options
The legend configuration is passed into the `options.legend` namespace. The global options for the chart legend is defined in `Chart.defaults.global.legend`.
| Name | Type | Default | Description
| -----| ---- | --------| -----------
| `display` | `Boolean` | `true` | is the legend shown
| `position` | `String` | `'top'` | Position of the legend. [more...](#position)
| `fullWidth` | `Boolean` | `true` | Marks that this box should take the full width of the canvas (pushing down other boxes). This is unlikely to need to be changed in day-to-day use.
| `onClick` | `Function` | | A callback that is called when a click event is registered on a label item
| `onHover` | `Function` | | A callback that is called when a 'mousemove' event is registered on top of a label item
| `reverse` | `Boolean` | `false` | Legend will show datasets in reverse order.
| `labels` | `Object` | | See the [Legend Label Configuration](#legend-label-configuration) section below.
## Position
Position of the legend. Options are:
* `'top'`
* `'left'`
* `'bottom'`
* `'right'`
## Legend Label Configuration
The legend label configuration is nested below the legend configuration using the `labels` key.
| Name | Type | Default | Description
| -----| ---- | --------| -----------
| `boxWidth` | `Number` | `40` | width of coloured box
| `fontSize` | `Number` | `12` | font size of text
| `fontStyle` | `String` | `'normal'` | font style of text
| `fontColor` | Color | `'#666'` | Color of text
| `fontFamily` | `String` | `"'Helvetica Neue', 'Helvetica', 'Arial', sans-serif"` | Font family of legend text.
| `padding` | `Number` | `10` | Padding between rows of colored boxes.
| `generateLabels` | `Function` | | Generates legend items for each thing in the legend. Default implementation returns the text + styling for the color box. See [Legend Item](#chart-configuration-legend-item-interface) for details.
| `filter` | `Function` | `null` | Filters legend items out of the legend. Receives 2 parameters, a [Legend Item](#chart-configuration-legend-item-interface) and the chart data.
| `usePointStyle` | `Boolean` | `false` | Label style will match corresponding point style (size is based on fontSize, boxWidth is not used in this case).
## Legend Item Interface
Items passed to the legend `onClick` function are the ones returned from `labels.generateLabels`. These items must implement the following interface.
```javascript
{
// Label that will be displayed
text: String,
// Fill style of the legend box
fillStyle: Color,
// If true, this item represents a hidden dataset. Label will be rendered with a strike-through effect
hidden: Boolean,
// For box border. See https://developer.mozilla.org/en/docs/Web/API/CanvasRenderingContext2D/lineCap
lineCap: String,
// For box border. See https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/setLineDash
lineDash: Array[Number],
// For box border. See https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/lineDashOffset
lineDashOffset: Number,
// For box border. See https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/lineJoin
lineJoin: String,
// Width of box border
lineWidth: Number,
// Stroke style of the legend box
strokeStyle: Color
// Point style of the legend box (only used if usePointStyle is true)
pointStyle: String
}
```
## Example
The following example will create a chart with the legend enabled and turn all of the text red in color.
```javascript
var chart = new Chart(ctx, {
type: 'bar',
data: data,
options: {
legend: {
display: true,
labels: {
fontColor: 'rgb(255, 99, 132)'
}
}
}
});
```
## Custom On Click Actions
It can be common to want to trigger different behaviour when clicking an item in the legend. This can be easily achieved using a callback in the config object.
The default legend click handler is:
```javascript
function(e, legendItem) {
var index = legendItem.datasetIndex;
var ci = this.chart;
var meta = ci.getDatasetMeta(index);
// See controller.isDatasetVisible comment
meta.hidden = meta.hidden === null? !ci.data.datasets[index].hidden : null;
// We hid a dataset ... rerender the chart
ci.update();
}
```
Lets say we wanted instead to link the display of the first two datasets. We could change the click handler accordingly.
```javascript
var defaultLegendClickHandler = Chart.defaults.global.legend.onClick;
var newLegendClickHandler = function (e, legendItem) {
var index = legendItem.datasetIndex;
if (index > 1) {
// Do the original logic
defaultLegendClickHandler(e, legendItem);
} else {
let ci = this.chart;
[ci.getDatasetMeta(0),
ci.getDatasetMeta(1)].forEach(function(meta) {
meta.hidden = meta.hidden === null? !ci.data.datasets[index].hidden : null;
});
ci.update();
}
};
var chart = new Chart(ctx, {
type: 'line',
data: data,
options: {
legend: {
}
}
});
```
Now when you click the legend in this chart, the visibility of the first two datasets will be linked together.
## HTML Legends
Sometimes you need a very complex legend. In these cases, it makes sense to generate an HTML legend. Charts provide a `generateLegend()` method on their prototype that returns an HTML string for the legend.
To configure how this legend is generated, you can change the `legendCallback` config property.
```javascript
var chart = new Chart(ctx, {
type: 'line',
data: data,
options: {
legendCallback: function(chart) {
// Return the HTML string here.
}
}
});
```
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