103 lines
4.1 KiB
Markdown
103 lines
4.1 KiB
Markdown
---
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id: 5a24c314108439a4d4036171
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title: Render State in the User Interface
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challengeType: 6
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isRequired: false
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forumTopicId: 301409
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---
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## Description
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<section id='description'>
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Once you define a component's initial state, you can display any part of it in the UI that is rendered. If a component is stateful, it will always have access to the data in <code>state</code> in its <code>render()</code> method. You can access the data with <code>this.state</code>.
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If you want to access a state value within the <code>return</code> of the render method, you have to enclose the value in curly braces.
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<code>State</code> is one of the most powerful features of components in React. It allows you to track important data in your app and render a UI in response to changes in this data. If your data changes, your UI will change. React uses what is called a virtual DOM, to keep track of changes behind the scenes. When state data updates, it triggers a re-render of the components using that data - including child components that received the data as a prop. React updates the actual DOM, but only where necessary. This means you don't have to worry about changing the DOM. You simply declare what the UI should look like.
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Note that if you make a component stateful, no other components are aware of its <code>state</code>. Its <code>state</code> is completely encapsulated, or local to that component, unless you pass state data to a child component as <code>props</code>. This notion of encapsulated <code>state</code> is very important because it allows you to write certain logic, then have that logic contained and isolated in one place in your code.
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</section>
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## Instructions
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<section id='instructions'>
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In the code editor, <code>MyComponent</code> is already stateful. Define an <code>h1</code> tag in the component's render method which renders the value of <code>name</code> from the component's state.
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<strong>Note:</strong> The <code>h1</code> should only render the value from <code>state</code> and nothing else. In JSX, any code you write with curly braces <code>{ }</code> will be treated as JavaScript. So to access the value from <code>state</code> just enclose the reference in curly braces.
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>MyComponent</code> should have a key <code>name</code> with value <code>freeCodeCamp</code> stored in its state.
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testString: assert(Enzyme.mount(React.createElement(MyComponent)).state('name') === 'freeCodeCamp');
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- text: <code>MyComponent</code> should render an <code>h1</code> header enclosed in a single <code>div</code>.
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testString: assert(/<div><h1>.*<\/h1><\/div>/.test(Enzyme.mount(React.createElement(MyComponent)).html()));
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- text: The rendered <code>h1</code> header should contain text rendered from the component's state.
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testString: 'async () => { const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250)); const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); const first = () => { mockedComponent.setState({ name: ''TestName'' }); return waitForIt(() => mockedComponent.html()) }; const firstValue = await first(); assert(firstValue === ''<div><h1>TestName</h1></div>'');};'
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='jsx-seed'>
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```jsx
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class MyComponent extends React.Component {
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constructor(props) {
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super(props);
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this.state = {
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name: 'freeCodeCamp'
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}
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}
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render() {
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return (
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<div>
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{ /* change code below this line */ }
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{ /* change code above this line */ }
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</div>
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);
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}
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};
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```
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</div>
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### After Test
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<div id='jsx-teardown'>
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```js
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ReactDOM.render(<MyComponent />, document.getElementById('root'))
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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class MyComponent extends React.Component {
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constructor(props) {
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super(props);
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this.state = {
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name: 'freeCodeCamp'
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}
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}
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render() {
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return (
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<div>
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{ /* change code below this line */ }
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<h1>{this.state.name}</h1>
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{ /* change code above this line */ }
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</div>
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);
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}
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};
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```
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</section>
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