147 lines
4.0 KiB
Markdown
147 lines
4.0 KiB
Markdown
---
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id: 5a24c314108439a4d4036177
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title: Write a Simple Counter
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challengeType: 6
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forumTopicId: 301425
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dashedName: write-a-simple-counter
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---
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# --description--
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You can design a more complex stateful component by combining the concepts covered so far. These include initializing `state`, writing methods that set `state`, and assigning click handlers to trigger these methods.
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# --instructions--
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The `Counter` component keeps track of a `count` value in `state`. There are two buttons which call methods `increment()` and `decrement()`. Write these methods so the counter value is incremented or decremented by 1 when the appropriate button is clicked. Also, create a `reset()` method so when the reset button is clicked, the count is set to 0.
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**Note:** Make sure you don't modify the `className`s of the buttons. Also, remember to add the necessary bindings for the newly-created methods in the constructor.
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# --hints--
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`Counter` should return a `div` element which contains three buttons with text content in this order `Increment!`, `Decrement!`, `Reset`.
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```js
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assert(
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(() => {
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const mockedComponent = Enzyme.mount(React.createElement(Counter));
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return (
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mockedComponent.find('.inc').text() === 'Increment!' &&
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mockedComponent.find('.dec').text() === 'Decrement!' &&
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mockedComponent.find('.reset').text() === 'Reset'
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);
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})()
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);
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```
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The state of `Counter` should initialize with a `count` property set to `0`.
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```js
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const mockedComponent = Enzyme.mount(React.createElement(Counter));
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assert(mockedComponent.find('h1').text() === 'Current Count: 0');
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```
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Clicking the increment button should increment the count by `1`.
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```js
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const mockedComponent = Enzyme.mount(React.createElement(Counter));
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mockedComponent.find('.inc').simulate('click');
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assert(mockedComponent.find('h1').text() === 'Current Count: 1');
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```
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Clicking the decrement button should decrement the count by `1`.
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```js
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const mockedComponent = Enzyme.mount(React.createElement(Counter));
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mockedComponent.find('.dec').simulate('click');
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assert(mockedComponent.find('h1').text() === 'Current Count: -1');
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```
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Clicking the reset button should reset the count to `0`.
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```js
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const mockedComponent = Enzyme.mount(React.createElement(Counter));
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mockedComponent.setState({ count: 5 });
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const currentCountElement = mockedComponent.find('h1');
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assert(currentCountElement.text() === 'Current Count: 5');
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mockedComponent.find('.reset').simulate('click');
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assert(currentCountElement.text() === 'Current Count: 0');
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```
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# --seed--
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## --after-user-code--
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```jsx
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ReactDOM.render(<Counter />, document.getElementById('root'))
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```
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## --seed-contents--
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```jsx
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class Counter 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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count: 0
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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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return (
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<div>
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<button className='inc' onClick={this.increment}>Increment!</button>
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<button className='dec' onClick={this.decrement}>Decrement!</button>
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<button className='reset' onClick={this.reset}>Reset</button>
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<h1>Current Count: {this.state.count}</h1>
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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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# --solutions--
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```jsx
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class Counter 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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count: 0
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};
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this.increment = this.increment.bind(this);
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this.decrement = this.decrement.bind(this);
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this.reset = this.reset.bind(this);
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}
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reset() {
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this.setState({
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count: 0
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});
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}
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increment() {
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this.setState(state => ({
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count: state.count + 1
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}));
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}
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decrement() {
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this.setState(state => ({
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count: state.count - 1
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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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<button className='inc' onClick={this.increment}>Increment!</button>
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<button className='dec' onClick={this.decrement}>Decrement!</button>
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<button className='reset' onClick={this.reset}>Reset</button>
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<h1>Current Count: {this.state.count}</h1>
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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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