freeCodeCamp/curriculum/challenges/chinese/04-data-visualization/data-visualization-with-d3/add-a-hover-effect-to-a-d3-...

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---
id: 587d7faa367417b2b2512bd4
title: Add a Hover Effect to a D3 Element
required:
- src: 'https://cdnjs.cloudflare.com/ajax/libs/d3/4.3.0/d3.min.js'
challengeType: 6
videoUrl: ''
localeTitle: 将悬停效果添加到D3元素
---
## Description
<section id="description">当用户用鼠标悬停在其上时可以添加突出显示条形的效果。到目前为止矩形的样式使用内置的D3和SVG方法但您也可以使用CSS。使用<code>attr()</code>方法在SVG元素上设置CSS类。然后新类的<code>:hover</code>伪类保存任何悬停效果的样式规则。 </section>
## Instructions
<section id="instructions">使用<code>attr()</code>方法向所有<code>rect</code>元素添加一个<code>bar</code>类。将鼠标悬停在其上时,会将条形的<code>fill</code>颜色更改为棕色。 </section>
## Tests
<section id='tests'>
```yml
tests:
- text: 你的<code>rect</code>元素应该有一类<code>bar</code>
testString: 'assert($("rect").attr("class") == "bar", "Your <code>rect</code> elements should have a class of <code>bar</code>.");'
```
</section>
## Challenge Seed
<section id='challengeSeed'>
<div id='html-seed'>
```html
<style>
.bar:hover {
fill: brown;
}
</style>
<body>
<script>
const dataset = [12, 31, 22, 17, 25, 18, 29, 14, 9];
const w = 500;
const h = 100;
const svg = d3.select("body")
.append("svg")
.attr("width", w)
.attr("height", h);
svg.selectAll("rect")
.data(dataset)
.enter()
.append("rect")
.attr("x", (d, i) => i * 30)
.attr("y", (d, i) => h - 3 * d)
.attr("width", 25)
.attr("height", (d, i) => 3 * d)
.attr("fill", "navy")
// Add your code below this line
// Add your code above this line
svg.selectAll("text")
.data(dataset)
.enter()
.append("text")
.text((d) => d)
.attr("x", (d, i) => i * 30)
.attr("y", (d, i) => h - (3 * d) - 3);
</script>
</body>
```
</div>
</section>
## Solution
<section id='solution'>
```js
// solution required
```
</section>