---
id: 5a24c314108439a4d403618b
title: Give Sibling Elements a Unique Key Attribute
challengeType: 6
forumTopicId: 301394
dashedName: give-sibling-elements-a-unique-key-attribute
---

# --description--

The last challenge showed how the `map` method is used to dynamically render a number of elements based on user input. However, there was an important piece missing from that example. When you create an array of elements, each one needs a `key` attribute set to a unique value. React uses these keys to keep track of which items are added, changed, or removed. This helps make the re-rendering process more efficient when the list is modified in any way.

**Note:** Keys only need to be unique between sibling elements, they don't need to be globally unique in your application.

# --instructions--

The code editor has an array with some front end frameworks and a stateless functional component named `Frameworks()`. `Frameworks()` needs to map the array to an unordered list, much like in the last challenge. Finish writing the `map` callback to return an `li` element for each framework in the `frontEndFrameworks` array. This time, make sure to give each `li` a `key` attribute, set to a unique value. The `li` elements should also contain text from `frontEndFrameworks`.

Normally, you want to make the key something that uniquely identifies the element being rendered. As a last resort the array index may be used, but typically you should try to use a unique identification.

# --hints--

The `Frameworks` component should exist and render to the page.

```js
assert(
  Enzyme.mount(React.createElement(Frameworks)).find('Frameworks').length === 1
);
```

`Frameworks` should render an `h1` element.

```js
assert(Enzyme.mount(React.createElement(Frameworks)).find('h1').length === 1);
```

`Frameworks` should render a `ul` element.

```js
assert(Enzyme.mount(React.createElement(Frameworks)).find('ul').length === 1);
```

The `ul` tag should render 6 child `li` elements.

```js
assert(
  Enzyme.mount(React.createElement(Frameworks)).find('ul').children().length ===
    6 &&
    Enzyme.mount(React.createElement(Frameworks))
      .find('ul')
      .childAt(0)
      .name() === 'li' &&
    Enzyme.mount(React.createElement(Frameworks)).find('li').length === 6
);
```

Each list item element should have a unique `key` attribute.

```js
assert(
  (() => {
    const ul = Enzyme.mount(React.createElement(Frameworks)).find('ul');
    const keys = new Set([
      ul.childAt(0).key(),
      ul.childAt(1).key(),
      ul.childAt(2).key(),
      ul.childAt(3).key(),
      ul.childAt(4).key(),
      ul.childAt(5).key()
    ]);
    return keys.size === 6;
  })()
);
```

Each list item element should contain text from `frontEndFrameworks`.

```js
assert(
  (() => {
    const li = Enzyme.mount(React.createElement(Frameworks))
      .find('ul')
      .children();
    return [...Array(5)].every((_, i) =>
      frontEndFrameworks.includes(li.at(i).text())
    );
  })()
);
```

# --seed--

## --after-user-code--

```jsx
ReactDOM.render(<Frameworks />, document.getElementById('root'))
```

## --seed-contents--

```jsx
const frontEndFrameworks = [
  'React',
  'Angular',
  'Ember',
  'Knockout',
  'Backbone',
  'Vue'
];

function Frameworks() {
  const renderFrameworks = null; // Change this line
  return (
    <div>
      <h1>Popular Front End JavaScript Frameworks</h1>
      <ul>
        {renderFrameworks}
      </ul>
    </div>
  );
};
```

# --solutions--

```jsx
const frontEndFrameworks = [
  'React',
  'Angular',
  'Ember',
  'Knockout',
  'Backbone',
  'Vue'
];

function Frameworks() {
  const renderFrameworks = frontEndFrameworks.map((fw, i) => <li key={i}>{fw}</li>);
  return (
    <div>
      <h1>Popular Front End JavaScript Frameworks</h1>
      <ul>
        {renderFrameworks}
      </ul>
    </div>
  );
};
```
