127 lines
4.8 KiB
Markdown
127 lines
4.8 KiB
Markdown
---
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id: 5a24c314108439a4d4036176
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title: Use State to Toggle an Element
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challengeType: 6
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isRequired: false
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---
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## Description
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<section id='description'>
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You can use <code>state</code> in React applications in more complex ways than what you've seen so far. One example is to monitor the status of a value, then render the UI conditionally based on this value. There are several different ways to accomplish this, and the code editor shows one method.
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</section>
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## Instructions
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<section id='instructions'>
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<code>MyComponent</code> has a <code>visibility</code> property which is initialized to <code>false</code>. The render method returns one view if the value of <code>visibility</code> is true, and a different view if it is false.
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Currently, there is no way of updating the <code>visibility</code> property in the component's <code>state</code>. The value should toggle back and forth between true and false. There is a click handler on the button which triggers a class method called <code>toggleVisibility()</code>. Define this method so the <code>state</code> of <code>visibility</code> toggles to the opposite value when the method is called. If <code>visibility</code> is <code>false</code>, the method sets it to <code>true</code>, and vice versa.
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Finally, click the button to see the conditional rendering of the component based on its <code>state</code>.
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<strong>Hint:</strong> Don't forget to bind the <code>this</code> keyword to the method in the constructor!
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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 return a <code>div</code> element which contains a <code>button</code>.
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testString: assert.strictEqual(Enzyme.mount(React.createElement(MyComponent)).find('div').find('button').length, 1, '<code>MyComponent</code> should return a <code>div</code> element which contains a <code>button</code>.');
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- text: The state of <code>MyComponent</code> should initialize with a <code>visibility</code> property set to <code>false</code>.
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testString: assert.strictEqual(Enzyme.mount(React.createElement(MyComponent)).state('visibility'), false, 'The state of <code>MyComponent</code> should initialize with a <code>visibility</code> property set to <code>false</code>.');
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- text: Clicking the button element should toggle the <code>visibility</code> property in state between <code>true</code> and <code>false</code>.
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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({ visibility: false }); return waitForIt(() => mockedComponent.state(''visibility'')); }; const second = () => { mockedComponent.find(''button'').simulate(''click''); return waitForIt(() => mockedComponent.state(''visibility'')); }; const third = () => { mockedComponent.find(''button'').simulate(''click''); return waitForIt(() => mockedComponent.state(''visibility'')); }; const firstValue = await first(); const secondValue = await second(); const thirdValue = await third(); assert(!firstValue && secondValue && !thirdValue, ''Clicking the button element should toggle the <code>visibility</code> property in state between <code>true</code> and <code>false</code>.''); }; '
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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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visibility: false
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};
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// change code below this line
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// change code above this line
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}
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// change code below this line
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// change code above this line
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render() {
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if (this.state.visibility) {
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return (
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<div>
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<button onClick={this.toggleVisibility}>Click Me</button>
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<h1>Now you see me!</h1>
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</div>
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);
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} else {
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return (
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<div>
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<button onClick={this.toggleVisibility}>Click Me</button>
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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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```
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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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visibility: false
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};
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this.toggleVisibility = this.toggleVisibility.bind(this);
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}
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toggleVisibility() {
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this.setState({
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visibility: !this.state.visibility
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});
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}
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render() {
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if (this.state.visibility) {
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return (
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<div>
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<button onClick = {this.toggleVisibility}>Click Me</button>
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<h1>Now you see me!</h1>
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</div>
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);
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} else {
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return (
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<div>
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<button onClick = {this.toggleVisibility}>Click Me</button>
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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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```
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</section>
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