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---
id: 587d7fa7367417b2b2512bc8
title: Add Classes with D3
challengeType: 6
forumTopicId: 301473
dashedName: add-classes-with-d3
---
# --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 `attr()` method to add any HTML attribute to an element, including a class name.
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The `attr()` method works the same way that `style()` 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:
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```js
selection.attr("class", "container");
```
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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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# --instructions--
Add the `attr()` method to the code in the editor and put a class of `bar` on the `div` elements.
# --hints--
Your `div` elements should have a class of `bar` .
```js
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assert($('div').attr('class').trim().split(/\s+/g).includes('bar'));
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```
Your code should use the `attr()` method.
```js
assert(code.match(/\.attr/g));
```
# --seed--
## --seed-contents--
```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
// Add your code above this line
< / script >
< / body >
```
# --solutions--
```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 >
```
