2018-09-30 23:01:58 +01:00
---
id: 587d7faa367417b2b2512bd4
title: Add a Hover Effect to a D3 Element
challengeType: 6
---
## 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
2018-10-04 14:37:37 +01:00
tests:
- text: Your < code > rect</ code > elements should have a class of < code > bar</ code > .
2019-07-11 01:53:41 -07:00
testString: assert($('rect').attr('class') == "bar");
2018-09-30 23:01:58 +01:00
```
< / 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];
2018-10-08 01:01:53 +01:00
2018-09-30 23:01:58 +01:00
const w = 500;
const h = 100;
2018-10-08 01:01:53 +01:00
2018-09-30 23:01:58 +01:00
const svg = d3.select("body")
.append("svg")
.attr("width", w)
.attr("height", h);
2018-10-08 01:01:53 +01:00
2018-09-30 23:01:58 +01:00
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
2018-10-08 01:01:53 +01:00
2018-09-30 23:01:58 +01:00
// Add your code above this line
2018-10-08 01:01:53 +01:00
2018-09-30 23:01:58 +01:00
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);
2018-10-08 01:01:53 +01:00
2018-09-30 23:01:58 +01:00
< / script >
< / body >
```
< / div >
< / section >
## Solution
< section id = 'solution' >
```js
2019-06-20 19:49:47 +03:00
< 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 >
2018-09-30 23:01:58 +01:00
```
2019-06-20 19:49:47 +03:00
2018-09-30 23:01:58 +01:00
< / section >
