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<section class="normal markdown-section">
<h1 id="legend-configuration">Legend Configuration</h1>
<p>The chart legend displays data about the datasets that area appearing on the chart.</p>
<h2 id="configuration-options">Configuration options</h2>
<p>The legend configuration is passed into the <code>options.legend</code> namespace. The global options for the chart legend is defined in <code>Chart.defaults.global.legend</code>.</p>
<table>
<thead>
<tr>
<th>Name</th>
<th>Type</th>
<th>Default</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>display</code></td>
<td><code>Boolean</code></td>
<td><code>true</code></td>
<td>is the legend shown</td>
</tr>
<tr>
<td><code>position</code></td>
<td><code>String</code></td>
<td><code>'top'</code></td>
<td>Position of the legend. <a href="#position">more...</a></td>
</tr>
<tr>
<td><code>fullWidth</code></td>
<td><code>Boolean</code></td>
<td><code>true</code></td>
<td>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.</td>
</tr>
<tr>
<td><code>onClick</code></td>
<td><code>Function</code></td>
<td></td>
<td>A callback that is called when a click event is registered on a label item</td>
</tr>
<tr>
<td><code>onHover</code></td>
<td><code>Function</code></td>
<td></td>
<td>A callback that is called when a 'mousemove' event is registered on top of a label item</td>
</tr>
<tr>
<td><code>reverse</code></td>
<td><code>Boolean</code></td>
<td><code>false</code></td>
<td>Legend will show datasets in reverse order.</td>
</tr>
<tr>
<td><code>labels</code></td>
<td><code>Object</code></td>
<td></td>
<td>See the <a href="#legend-label-configuration">Legend Label Configuration</a> section below.</td>
</tr>
</tbody>
</table>
<h2 id="position">Position</h2>
<p>Position of the legend. Options are:</p>
<ul>
<li><code>'top'</code></li>
<li><code>'left'</code></li>
<li><code>'bottom'</code></li>
<li><code>'right'</code></li>
</ul>
<h2 id="legend-label-configuration">Legend Label Configuration</h2>
<p>The legend label configuration is nested below the legend configuration using the <code>labels</code> key.</p>
<table>
<thead>
<tr>
<th>Name</th>
<th>Type</th>
<th>Default</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>boxWidth</code></td>
<td><code>Number</code></td>
<td><code>40</code></td>
<td>width of coloured box</td>
</tr>
<tr>
<td><code>fontSize</code></td>
<td><code>Number</code></td>
<td><code>12</code></td>
<td>font size of text</td>
</tr>
<tr>
<td><code>fontStyle</code></td>
<td><code>String</code></td>
<td><code>'normal'</code></td>
<td>font style of text</td>
</tr>
<tr>
<td><code>fontColor</code></td>
<td><code>Color</code></td>
<td><code>'#666'</code></td>
<td>Color of text</td>
</tr>
<tr>
<td><code>fontFamily</code></td>
<td><code>String</code></td>
<td><code>"'Helvetica Neue', 'Helvetica', 'Arial', sans-serif"</code></td>
<td>Font family of legend text.</td>
</tr>
<tr>
<td><code>padding</code></td>
<td><code>Number</code></td>
<td><code>10</code></td>
<td>Padding between rows of colored boxes.</td>
</tr>
<tr>
<td><code>generateLabels</code></td>
<td><code>Function</code></td>
<td></td>
<td>Generates legend items for each thing in the legend. Default implementation returns the text + styling for the color box. See <a href="#legend-item-interface">Legend Item</a> for details.</td>
</tr>
<tr>
<td><code>filter</code></td>
<td><code>Function</code></td>
<td><code>null</code></td>
<td>Filters legend items out of the legend. Receives 2 parameters, a <a href="#legend-item-interface">Legend Item</a> and the chart data.</td>
</tr>
<tr>
<td><code>usePointStyle</code></td>
<td><code>Boolean</code></td>
<td><code>false</code></td>
<td>Label style will match corresponding point style (size is based on fontSize, boxWidth is not used in this case).</td>
</tr>
</tbody>
</table>
<h2 id="legend-item-interface">Legend Item Interface</h2>
<p>Items passed to the legend <code>onClick</code> function are the ones returned from <code>labels.generateLabels</code>. These items must implement the following interface.</p>
<pre><code class="lang-javascript">{
<span class="hljs-comment">// Label that will be displayed</span>
text: <span class="hljs-built_in">String</span>,
<span class="hljs-comment">// Fill style of the legend box</span>
fillStyle: Color,
<span class="hljs-comment">// If true, this item represents a hidden dataset. Label will be rendered with a strike-through effect</span>
hidden: <span class="hljs-built_in">Boolean</span>,
<span class="hljs-comment">// For box border. See https://developer.mozilla.org/en/docs/Web/API/CanvasRenderingContext2D/lineCap</span>
lineCap: <span class="hljs-built_in">String</span>,
<span class="hljs-comment">// For box border. See https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/setLineDash</span>
lineDash: <span class="hljs-built_in">Array</span>[<span class="hljs-built_in">Number</span>],
<span class="hljs-comment">// For box border. See https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/lineDashOffset</span>
lineDashOffset: <span class="hljs-built_in">Number</span>,
<span class="hljs-comment">// For box border. See https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/lineJoin</span>
lineJoin: <span class="hljs-built_in">String</span>,
<span class="hljs-comment">// Width of box border</span>
lineWidth: <span class="hljs-built_in">Number</span>,
<span class="hljs-comment">// Stroke style of the legend box</span>
strokeStyle: Color
<span class="hljs-comment">// Point style of the legend box (only used if usePointStyle is true)</span>
pointStyle: <span class="hljs-built_in">String</span>
}
</code></pre>
<h2 id="example">Example</h2>
<p>The following example will create a chart with the legend enabled and turn all of the text red in color.</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">var</span> chart = <span class="hljs-keyword">new</span> Chart(ctx, {
type: <span class="hljs-string">'bar'</span>,
data: data,
options: {
legend: {
display: <span class="hljs-literal">true</span>,
labels: {
fontColor: <span class="hljs-string">'rgb(255, 99, 132)'</span>
}
}
}
});
</code></pre>
<h2 id="custom-on-click-actions">Custom On Click Actions</h2>
<p>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.</p>
<p>The default legend click handler is:</p>
<pre><code class="lang-javascript"><span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params">e, legendItem</span>) </span>{
<span class="hljs-keyword">var</span> index = legendItem.datasetIndex;
<span class="hljs-keyword">var</span> ci = <span class="hljs-keyword">this</span>.chart;
<span class="hljs-keyword">var</span> meta = ci.getDatasetMeta(index);
<span class="hljs-comment">// See controller.isDatasetVisible comment</span>
meta.hidden = meta.hidden === <span class="hljs-literal">null</span>? !ci.data.datasets[index].hidden : <span class="hljs-literal">null</span>;
<span class="hljs-comment">// We hid a dataset ... rerender the chart</span>
ci.update();
}
</code></pre>
<p>Lets say we wanted instead to link the display of the first two datasets. We could change the click handler accordingly.</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">var</span> defaultLegendClickHandler = Chart.defaults.global.legend.onClick;
<span class="hljs-keyword">var</span> newLegendClickHandler = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params">e, legendItem</span>) </span>{
<span class="hljs-keyword">var</span> index = legendItem.datasetIndex;
<span class="hljs-keyword">if</span> (index > <span class="hljs-number">1</span>) {
<span class="hljs-comment">// Do the original logic</span>
defaultLegendClickHandler(e, legendItem);
} <span class="hljs-keyword">else</span> {
<span class="hljs-keyword">let</span> ci = <span class="hljs-keyword">this</span>.chart;
[ci.getDatasetMeta(<span class="hljs-number">0</span>),
ci.getDatasetMeta(<span class="hljs-number">1</span>)].forEach(<span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params">meta</span>) </span>{
meta.hidden = meta.hidden === <span class="hljs-literal">null</span>? !ci.data.datasets[index].hidden : <span class="hljs-literal">null</span>;
});
ci.update();
}
};
<span class="hljs-keyword">var</span> chart = <span class="hljs-keyword">new</span> Chart(ctx, {
type: <span class="hljs-string">'line'</span>,
data: data,
options: {
legend: {
}
}
});
</code></pre>
<p>Now when you click the legend in this chart, the visibility of the first two datasets will be linked together.</p>
<h2 id="html-legends">HTML Legends</h2>
<p>Sometimes you need a very complex legend. In these cases, it makes sense to generate an HTML legend. Charts provide a <code>generateLegend()</code> method on their prototype that returns an HTML string for the legend.</p>
<p>To configure how this legend is generated, you can change the <code>legendCallback</code> config property.</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">var</span> chart = <span class="hljs-keyword">new</span> Chart(ctx, {
type: <span class="hljs-string">'line'</span>,
data: data,
options: {
legendCallback: <span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params">chart</span>) </span>{
<span class="hljs-comment">// Return the HTML string here.</span>
}
}
});
</code></pre>
<p>Note that legendCallback is not called automatically and you must call <code>generateLegend()</code> yourself in code when creating a legend using this method.</p>
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