112 lines
4.5 KiB
Markdown
112 lines
4.5 KiB
Markdown
---
|
|
id: 5a24c314108439a4d403618b
|
|
title: Give Sibling Elements a Unique Key Attribute
|
|
challengeType: 6
|
|
isRequired: false
|
|
---
|
|
|
|
## Description
|
|
<section id='description'>
|
|
The last challenge showed how the <code>map</code> 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 <code>key</code> 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.<br><br><strong>Note:</strong> Keys only need to be unique between sibling elements, they don't need to be globally unique in your application.
|
|
</section>
|
|
|
|
## Instructions
|
|
<section id='instructions'>
|
|
The code editor has an array with some front end frameworks and a stateless functional component named <code>Frameworks()</code>. <code>Frameworks()</code> needs to map the array to an unordered list, much like in the last challenge. Finish writing the <code>map</code> callback to return an <code>li</code> element for each framework in the <code>frontEndFrameworks</code> array. This time, make sure to give each <code>li</code> a <code>key</code> attribute, set to a unique value. The <code>li</code> elements should also contain text from <code>frontEndFrameworks</code>.
|
|
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.
|
|
</section>
|
|
|
|
## Tests
|
|
<section id='tests'>
|
|
|
|
```yml
|
|
tests:
|
|
- text: The <code>Frameworks</code> component should exist and render to the page.
|
|
testString: assert(Enzyme.mount(React.createElement(Frameworks)).find('Frameworks').length === 1, 'The <code>Frameworks</code> component should exist and render to the page.');
|
|
- text: <code>Frameworks</code> should render an <code>h1</code> element.
|
|
testString: assert(Enzyme.mount(React.createElement(Frameworks)).find('h1').length === 1, '<code>Frameworks</code> should render an <code>h1</code> element.');
|
|
- text: <code>Frameworks</code> should render a <code>ul</code> element.
|
|
testString: assert(Enzyme.mount(React.createElement(Frameworks)).find('ul').length === 1, '<code>Frameworks</code> should render a <code>ul</code> element.');
|
|
- text: The <code>ul</code> tag should render 6 child <code>li</code> elements.
|
|
testString: 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, 'The <code>ul</code> tag should render 6 child <code>li</code> elements.');
|
|
- text: Each list item element should have a unique <code>key</code> attribute.
|
|
testString: 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 have a unique <code>key</code> attribute.');
|
|
- text: Each list item element should contain text from <code>frontEndFrameworks</code>.
|
|
testString: assert((() => {const li = Enzyme.mount(React.createElement(Frameworks)).find('ul').children(); return [...Array(5)].every((_, i) => frontEndFrameworks.includes(li.at(i).text()))})(), 'Each list item element should contain text from <code>frontEndFrameworks</code');
|
|
|
|
```
|
|
|
|
</section>
|
|
|
|
## Challenge Seed
|
|
<section id='challengeSeed'>
|
|
|
|
<div id='jsx-seed'>
|
|
|
|
```jsx
|
|
|
|
const frontEndFrameworks = [
|
|
'React',
|
|
'Angular',
|
|
'Ember',
|
|
'Knockout',
|
|
'Backbone',
|
|
'Vue'
|
|
];
|
|
|
|
function Frameworks() {
|
|
const renderFrameworks = null; // change code here
|
|
return (
|
|
<div>
|
|
<h1>Popular Front End JavaScript Frameworks</h1>
|
|
<ul>
|
|
{renderFrameworks}
|
|
</ul>
|
|
</div>
|
|
);
|
|
};
|
|
```
|
|
|
|
</div>
|
|
|
|
|
|
### After Test
|
|
<div id='jsx-teardown'>
|
|
|
|
```js
|
|
ReactDOM.render(<Frameworks />, document.getElementById('root'))
|
|
```
|
|
|
|
</div>
|
|
|
|
</section>
|
|
|
|
## Solution
|
|
<section id='solution'>
|
|
|
|
|
|
```js
|
|
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>
|
|
);
|
|
};
|
|
```
|
|
|
|
</section>
|