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---
id: 587d7fa7367417b2b2512bc8
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title: Add Classes with D3
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challengeType: 6
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forumTopicId: 301473
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dashedName: add-classes-with-d3
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---
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# --description--
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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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`selection.attr("class", "container");`
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--
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Add the `attr()` method to the code in the editor and put a class of `bar` on the `div` elements.
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# --hints--
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Your `div` elements should have a class of `bar` .
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```js
assert($('div').attr('class') == 'bar');
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```
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Your code should use the `attr()` method.
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```js
assert(code.match(/\.attr/g));
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```
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# --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 >
```
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# --solutions--
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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 >
```
