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  242. Labelling
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  269. Plugins
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  291. Additional Notes
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  323. <!-- Title -->
  324. <h1>
  325. <i class="fa fa-circle-o-notch fa-spin"></i>
  326. <a href=".." >Legend</a>
  327. </h1>
  328. </div>
  329. <div class="page-wrapper" tabindex="-1" role="main">
  330. <div class="page-inner">
  331. <div class="search-plus" id="book-search-results">
  332. <div class="search-noresults">
  333. <section class="normal markdown-section">
  334. <h1 id="legend-configuration">Legend Configuration</h1>
  335. <p>The chart legend displays data about the datasets that area appearing on the chart.</p>
  336. <h2 id="configuration-options">Configuration options</h2>
  337. <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>
  338. <table>
  339. <thead>
  340. <tr>
  341. <th>Name</th>
  342. <th>Type</th>
  343. <th>Default</th>
  344. <th>Description</th>
  345. </tr>
  346. </thead>
  347. <tbody>
  348. <tr>
  349. <td><code>display</code></td>
  350. <td><code>Boolean</code></td>
  351. <td><code>true</code></td>
  352. <td>is the legend shown</td>
  353. </tr>
  354. <tr>
  355. <td><code>position</code></td>
  356. <td><code>String</code></td>
  357. <td><code>&apos;top&apos;</code></td>
  358. <td>Position of the legend. <a href="#position">more...</a></td>
  359. </tr>
  360. <tr>
  361. <td><code>fullWidth</code></td>
  362. <td><code>Boolean</code></td>
  363. <td><code>true</code></td>
  364. <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>
  365. </tr>
  366. <tr>
  367. <td><code>onClick</code></td>
  368. <td><code>Function</code></td>
  369. <td></td>
  370. <td>A callback that is called when a click event is registered on a label item </td>
  371. </tr>
  372. <tr>
  373. <td><code>onHover</code></td>
  374. <td><code>Function</code></td>
  375. <td></td>
  376. <td>A callback that is called when a &apos;mousemove&apos; event is registered on top of a label item</td>
  377. </tr>
  378. <tr>
  379. <td><code>reverse</code></td>
  380. <td><code>Boolean</code></td>
  381. <td><code>false</code></td>
  382. <td>Legend will show datasets in reverse order.</td>
  383. </tr>
  384. <tr>
  385. <td><code>labels</code></td>
  386. <td><code>Object</code></td>
  387. <td></td>
  388. <td>See the <a href="#legend-label-configuration">Legend Label Configuration</a> section below.</td>
  389. </tr>
  390. </tbody>
  391. </table>
  392. <h2 id="position">Position</h2>
  393. <p>Position of the legend. Options are:</p>
  394. <ul>
  395. <li><code>&apos;top&apos;</code></li>
  396. <li><code>&apos;left&apos;</code></li>
  397. <li><code>&apos;bottom&apos;</code></li>
  398. <li><code>&apos;right&apos;</code></li>
  399. </ul>
  400. <h2 id="legend-label-configuration">Legend Label Configuration</h2>
  401. <p>The legend label configuration is nested below the legend configuration using the <code>labels</code> key.</p>
  402. <table>
  403. <thead>
  404. <tr>
  405. <th>Name</th>
  406. <th>Type</th>
  407. <th>Default</th>
  408. <th>Description</th>
  409. </tr>
  410. </thead>
  411. <tbody>
  412. <tr>
  413. <td><code>boxWidth</code></td>
  414. <td><code>Number</code></td>
  415. <td><code>40</code></td>
  416. <td>width of coloured box</td>
  417. </tr>
  418. <tr>
  419. <td><code>fontSize</code></td>
  420. <td><code>Number</code></td>
  421. <td><code>12</code></td>
  422. <td>font size of text</td>
  423. </tr>
  424. <tr>
  425. <td><code>fontStyle</code></td>
  426. <td><code>String</code></td>
  427. <td><code>&apos;normal&apos;</code></td>
  428. <td>font style of text</td>
  429. </tr>
  430. <tr>
  431. <td><code>fontColor</code></td>
  432. <td><code>Color</code></td>
  433. <td><code>&apos;#666&apos;</code></td>
  434. <td>Color of text</td>
  435. </tr>
  436. <tr>
  437. <td><code>fontFamily</code></td>
  438. <td><code>String</code></td>
  439. <td><code>&quot;&apos;Helvetica Neue&apos;, &apos;Helvetica&apos;, &apos;Arial&apos;, sans-serif&quot;</code></td>
  440. <td>Font family of legend text.</td>
  441. </tr>
  442. <tr>
  443. <td><code>padding</code></td>
  444. <td><code>Number</code></td>
  445. <td><code>10</code></td>
  446. <td>Padding between rows of colored boxes.</td>
  447. </tr>
  448. <tr>
  449. <td><code>generateLabels</code></td>
  450. <td><code>Function</code></td>
  451. <td></td>
  452. <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>
  453. </tr>
  454. <tr>
  455. <td><code>filter</code></td>
  456. <td><code>Function</code></td>
  457. <td><code>null</code></td>
  458. <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>
  459. </tr>
  460. <tr>
  461. <td><code>usePointStyle</code></td>
  462. <td><code>Boolean</code></td>
  463. <td><code>false</code></td>
  464. <td>Label style will match corresponding point style (size is based on fontSize, boxWidth is not used in this case).</td>
  465. </tr>
  466. </tbody>
  467. </table>
  468. <h2 id="legend-item-interface">Legend Item Interface</h2>
  469. <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>
  470. <pre><code class="lang-javascript">{
  471. <span class="hljs-comment">// Label that will be displayed</span>
  472. text: <span class="hljs-built_in">String</span>,
  473. <span class="hljs-comment">// Fill style of the legend box</span>
  474. fillStyle: Color,
  475. <span class="hljs-comment">// If true, this item represents a hidden dataset. Label will be rendered with a strike-through effect</span>
  476. hidden: <span class="hljs-built_in">Boolean</span>,
  477. <span class="hljs-comment">// For box border. See https://developer.mozilla.org/en/docs/Web/API/CanvasRenderingContext2D/lineCap</span>
  478. lineCap: <span class="hljs-built_in">String</span>,
  479. <span class="hljs-comment">// For box border. See https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/setLineDash</span>
  480. lineDash: <span class="hljs-built_in">Array</span>[<span class="hljs-built_in">Number</span>],
  481. <span class="hljs-comment">// For box border. See https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/lineDashOffset</span>
  482. lineDashOffset: <span class="hljs-built_in">Number</span>,
  483. <span class="hljs-comment">// For box border. See https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/lineJoin</span>
  484. lineJoin: <span class="hljs-built_in">String</span>,
  485. <span class="hljs-comment">// Width of box border</span>
  486. lineWidth: <span class="hljs-built_in">Number</span>,
  487. <span class="hljs-comment">// Stroke style of the legend box</span>
  488. strokeStyle: Color
  489. <span class="hljs-comment">// Point style of the legend box (only used if usePointStyle is true)</span>
  490. pointStyle: <span class="hljs-built_in">String</span>
  491. }
  492. </code></pre>
  493. <h2 id="example">Example</h2>
  494. <p>The following example will create a chart with the legend enabled and turn all of the text red in color.</p>
  495. <pre><code class="lang-javascript"><span class="hljs-keyword">var</span> chart = <span class="hljs-keyword">new</span> Chart(ctx, {
  496. type: <span class="hljs-string">&apos;bar&apos;</span>,
  497. data: data,
  498. options: {
  499. legend: {
  500. display: <span class="hljs-literal">true</span>,
  501. labels: {
  502. fontColor: <span class="hljs-string">&apos;rgb(255, 99, 132)&apos;</span>
  503. }
  504. }
  505. }
  506. });
  507. </code></pre>
  508. <h2 id="custom-on-click-actions">Custom On Click Actions</h2>
  509. <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>
  510. <p>The default legend click handler is:</p>
  511. <pre><code class="lang-javascript"><span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params">e, legendItem</span>) </span>{
  512. <span class="hljs-keyword">var</span> index = legendItem.datasetIndex;
  513. <span class="hljs-keyword">var</span> ci = <span class="hljs-keyword">this</span>.chart;
  514. <span class="hljs-keyword">var</span> meta = ci.getDatasetMeta(index);
  515. <span class="hljs-comment">// See controller.isDatasetVisible comment</span>
  516. meta.hidden = meta.hidden === <span class="hljs-literal">null</span>? !ci.data.datasets[index].hidden : <span class="hljs-literal">null</span>;
  517. <span class="hljs-comment">// We hid a dataset ... rerender the chart</span>
  518. ci.update();
  519. }
  520. </code></pre>
  521. <p>Lets say we wanted instead to link the display of the first two datasets. We could change the click handler accordingly.</p>
  522. <pre><code class="lang-javascript"><span class="hljs-keyword">var</span> defaultLegendClickHandler = Chart.defaults.global.legend.onClick;
  523. <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>{
  524. <span class="hljs-keyword">var</span> index = legendItem.datasetIndex;
  525. <span class="hljs-keyword">if</span> (index &gt; <span class="hljs-number">1</span>) {
  526. <span class="hljs-comment">// Do the original logic</span>
  527. defaultLegendClickHandler(e, legendItem);
  528. } <span class="hljs-keyword">else</span> {
  529. <span class="hljs-keyword">let</span> ci = <span class="hljs-keyword">this</span>.chart;
  530. [ci.getDatasetMeta(<span class="hljs-number">0</span>),
  531. 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>{
  532. meta.hidden = meta.hidden === <span class="hljs-literal">null</span>? !ci.data.datasets[index].hidden : <span class="hljs-literal">null</span>;
  533. });
  534. ci.update();
  535. }
  536. };
  537. <span class="hljs-keyword">var</span> chart = <span class="hljs-keyword">new</span> Chart(ctx, {
  538. type: <span class="hljs-string">&apos;line&apos;</span>,
  539. data: data,
  540. options: {
  541. legend: {
  542. }
  543. }
  544. });
  545. </code></pre>
  546. <p>Now when you click the legend in this chart, the visibility of the first two datasets will be linked together.</p>
  547. <h2 id="html-legends">HTML Legends</h2>
  548. <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>
  549. <p>To configure how this legend is generated, you can change the <code>legendCallback</code> config property.</p>
  550. <pre><code class="lang-javascript"><span class="hljs-keyword">var</span> chart = <span class="hljs-keyword">new</span> Chart(ctx, {
  551. type: <span class="hljs-string">&apos;line&apos;</span>,
  552. data: data,
  553. options: {
  554. legendCallback: <span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params">chart</span>) </span>{
  555. <span class="hljs-comment">// Return the HTML string here.</span>
  556. }
  557. }
  558. });
  559. </code></pre>
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