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---
id: 587d7fa7367417b2b2512bc8
title: Add Classes with D3
challengeType: 6
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forumTopicId: 301473
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---
## Description
< section id = 'description' >
Using a lot of inline styles on HTML elements gets hard to manage, even for smaller apps. It's easier to add a class to elements and style that class one time using CSS rules. D3 has the < code > attr()< / code > method to add any HTML attribute to an element, including a class name.
The < code > attr()< / code > method works the same way that < code > style()< / code > does. It takes comma-separated values, and can use a callback function. Here's an example to add a class of "container" to a selection:
< code > selection.attr("class", "container");< / code >
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Note that the "class" parameter will remain the same whenever you need to add a class and only the "container" parameter will change.
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< / section >
## Instructions
< section id = 'instructions' >
Add the < code > attr()< / code > method to the code in the editor and put a class of < code > bar< / code > on the < code > div< / code > elements.
< / section >
## Tests
< section id = 'tests' >
```yml
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tests:
- text: Your < code > div</ code > elements should have a class of < code > bar</ code > .
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testString: assert($('div').attr('class') == "bar");
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- text: Your code should use the < code > attr()</ code > method.
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testString: assert(code.match(/\.attr/g));
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```
< / section >
## Challenge Seed
< section id = 'challengeSeed' >
< div id = 'html-seed' >
```html
< style >
.bar {
width: 25px;
height: 100px;
display: inline-block;
background-color: blue;
}
< / style >
< body >
< script >
const dataset = [12, 31, 22, 17, 25, 18, 29, 14, 9];
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d3.select("body").selectAll("div")
.data(dataset)
.enter()
.append("div")
// Add your code below this line
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// Add your code above this line
< / script >
< / body >
```
< / div >
< / section >
## Solution
< section id = 'solution' >
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```html
< style >
.bar {
width: 25px;
height: 100px;
display: inline-block;
background-color: blue;
}
< / style >
< body >
< script >
const dataset = [12, 31, 22, 17, 25, 18, 29, 14, 9];
d3.select("body").selectAll("div")
.data(dataset)
.enter()
.append("div")
// Add your code below this line
.attr("class","bar");
// Add your code above this line
< / script >
< / body >
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```
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< / section >
