177 lines
6.7 KiB
Markdown
177 lines
6.7 KiB
Markdown
---
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id: 5a24c314108439a4d403617b
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title: Pass a Callback as Props
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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 pass <code>state</code> as props to child components, but you're not limited to passing data. You can also pass handler functions or any method that's defined on a React component to a child component. This is how you allow child components to interact with their parent components. You pass methods to a child just like a regular prop. It's assigned a name and you have access to that method name under <code>this.props</code> in the child component.
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</section>
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## Instructions
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<section id='instructions'>
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There are three components outlined in the code editor. The <code>MyApp</code> component is the parent that will render the <code>GetInput</code> and <code>RenderInput</code> child components. Add the <code>GetInput</code> component to the render method in <code>MyApp</code>, then pass it a prop called <code>input</code> assigned to <code>inputValue</code> from <code>MyApp</code>'s <code>state</code>. Also create a prop called <code>handleChange</code> and pass the input handler <code>handleChange</code> to it.
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Next, add <code>RenderInput</code> to the render method in <code>MyApp</code>, then create a prop called <code>input</code> and pass the <code>inputValue</code> from <code>state</code> to it. Once you are finished you will be able to type in the <code>input</code> field in the <code>GetInput</code> component, which then calls the handler method in its parent via props. This updates the input in the <code>state</code> of the parent, which is passed as props to both children. Observe how the data flows between the components and how the single source of truth remains the <code>state</code> of the parent component. Admittedly, this example is a bit contrived, but should serve to illustrate how data and callbacks can be passed between React components.
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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: The <code>MyApp</code> component should render.
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testString: assert((function() { const mockedComponent = Enzyme.mount(React.createElement(MyApp)); return mockedComponent.find('MyApp').length === 1; })(), 'The <code>MyApp</code> component should render.');
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- text: The <code>GetInput</code> component should render.
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testString: assert((function() { const mockedComponent = Enzyme.mount(React.createElement(MyApp)); return mockedComponent.find('GetInput').length === 1; })(), 'The <code>GetInput</code> component should render.');
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- text: The <code>RenderInput</code> component should render.
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testString: assert((function() { const mockedComponent = Enzyme.mount(React.createElement(MyApp)); return mockedComponent.find('RenderInput').length === 1; })(), 'The <code>RenderInput</code> component should render.');
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- text: The <code>GetInput</code> component should receive the <code>MyApp</code> state property <code>inputValue</code> as props and contain an <code>input</code> element which modifies <code>MyApp</code> state.
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testString: 'async () => { const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250)); const mockedComponent = Enzyme.mount(React.createElement(MyApp)); const state_1 = () => { mockedComponent.setState({inputValue: ''''}); return waitForIt(() => mockedComponent.state() )}; const state_2 = () => { mockedComponent.find(''input'').simulate(''change'', {target: {value: ''TestInput''}}); return waitForIt(() => mockedComponent.state() )}; const updated_1 = await state_1(); const updated_2 = await state_2(); assert(updated_1.inputValue === '''' && updated_2.inputValue === ''TestInput'', ''The <code>GetInput</code> component should receive the <code>MyApp</code> state property <code>inputValue</code> as props and contain an <code>input</code> element which modifies <code>MyApp</code> state.''); }; '
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- text: The <code>RenderInput</code> component should receive the <code>MyApp</code> state property <code>inputValue</code> as props.
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testString: 'async () => { const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250)); const mockedComponent = Enzyme.mount(React.createElement(MyApp)); const state_1 = () => { mockedComponent.setState({inputValue: ''TestName''}); return waitForIt(() => mockedComponent )}; const updated_1 = await state_1(); assert(updated_1.find(''p'').text().includes(''TestName''), ''The <code>RenderInput</code> component should receive the <code>MyApp</code> state property <code>inputValue</code> as props.''); }; '
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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 MyApp 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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inputValue: ''
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}
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this.handleChange = this.handleChange.bind(this);
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}
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handleChange(event) {
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this.setState({
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inputValue: event.target.value
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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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class GetInput extends React.Component {
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constructor(props) {
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super(props);
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}
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render() {
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return (
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<div>
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<h3>Get Input:</h3>
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<input
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value={this.props.input}
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onChange={this.props.handleChange}/>
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</div>
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);
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}
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};
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class RenderInput extends React.Component {
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constructor(props) {
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super(props);
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}
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render() {
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return (
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<div>
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<h3>Input Render:</h3>
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<p>{this.props.input}</p>
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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(<MyApp />, 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 MyApp 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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inputValue: ''
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}
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this.handleChange = this.handleChange.bind(this);
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}
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handleChange(event) {
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this.setState({
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inputValue: event.target.value
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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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<GetInput
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input={this.state.inputValue}
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handleChange={this.handleChange}/>
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<RenderInput
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input={this.state.inputValue}/>
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</div>
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);
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}
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};
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class GetInput extends React.Component {
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constructor(props) {
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super(props);
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}
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render() {
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return (
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<div>
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<h3>Get Input:</h3>
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<input
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value={this.props.input}
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onChange={this.props.handleChange}/>
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</div>
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);
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}
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};
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class RenderInput extends React.Component {
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constructor(props) {
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super(props);
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}
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render() {
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return (
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<div>
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<h3>Input Render:</h3>
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<p>{this.props.input}</p>
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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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