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---
id: 587d7faa367417b2b2512bd4
title: Add a Hover Effect to a D3 Element
challengeType: 6
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forumTopicId: 301469
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---
## Description
< section id = 'description' >
It's possible to add effects that highlight a bar when the user hovers over it with the mouse. So far, the styling for the rectangles is applied with the built-in D3 and SVG methods, but you can use CSS as well.
You set the CSS class on the SVG elements with the < code > attr()< / code > method. Then the < code > :hover< / code > pseudo-class for your new class holds the style rules for any hover effects.
< / section >
## Instructions
< section id = 'instructions' >
Use the < code > attr()< / code > method to add a class of < code > bar< / code > to all the < code > rect< / code > elements. This changes the < code > fill< / code > color of the bar to brown when you mouse over it.
< / section >
## Tests
< section id = 'tests' >
```yml
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tests:
- text: Your < code > rect</ code > elements should have a class of < code > bar</ code > .
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testString: assert($('rect').attr('class') == "bar");
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```
< / 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];
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const w = 500;
const h = 100;
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const svg = d3.select("body")
.append("svg")
.attr("width", w)
.attr("height", h);
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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
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// Add your code above this line
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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);
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< / script >
< / body >
```
< / div >
< / section >
## Solution
< section id = 'solution' >
```js
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< 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
.attr('class', 'bar')
// 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 >
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```
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< / section >
