freeCodeCamp/curriculum/challenges/english/03-front-end-libraries/react/write-a-simple-counter.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
5a24c314108439a4d4036177	Write a Simple Counter	6	301425	write-a-simple-counter

--description--

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.

--instructions--

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.

Note: Make sure you don't modify the classNames of the buttons. Also, remember to add the necessary bindings for the newly-created methods in the constructor.

--hints--

Counter should return a div element which contains three buttons with text content in this order Increment!, Decrement!, Reset.

assert(
  (() => {
    const mockedComponent = Enzyme.mount(React.createElement(Counter));
    return (
      mockedComponent.find('.inc').text() === 'Increment!' &&
      mockedComponent.find('.dec').text() === 'Decrement!' &&
      mockedComponent.find('.reset').text() === 'Reset'
    );
  })()
);

The state of Counter should initialize with a count property set to 0.

const mockedComponent = Enzyme.mount(React.createElement(Counter));
assert(mockedComponent.find('h1').text() === 'Current Count: 0');

Clicking the increment button should increment the count by 1.

const mockedComponent = Enzyme.mount(React.createElement(Counter));
mockedComponent.find('.inc').simulate('click');
assert(mockedComponent.find('h1').text() === 'Current Count: 1');

Clicking the decrement button should decrement the count by 1.

const mockedComponent = Enzyme.mount(React.createElement(Counter));
mockedComponent.find('.dec').simulate('click');
assert(mockedComponent.find('h1').text() === 'Current Count: -1');

Clicking the reset button should reset the count to 0.

const mockedComponent = Enzyme.mount(React.createElement(Counter));
mockedComponent.setState({ count: 5 });
const currentCountElement = mockedComponent.find('h1');
assert(currentCountElement.text() === 'Current Count: 5');
mockedComponent.find('.reset').simulate('click');
assert(currentCountElement.text() === 'Current Count: 0');

--seed--

--after-user-code--

ReactDOM.render(<Counter />, document.getElementById('root'))

--seed-contents--

class Counter extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };
    // Change code below this line

    // Change code above this line
  }
  // Change code below this line

  // Change code above this line
  render() {
    return (
      <div>
        <button className='inc' onClick={this.increment}>Increment!</button>
        <button className='dec' onClick={this.decrement}>Decrement!</button>
        <button className='reset' onClick={this.reset}>Reset</button>
        <h1>Current Count: {this.state.count}</h1>
      </div>
    );
  }
};

--solutions--

class Counter extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };
  this.increment = this.increment.bind(this);
 this.decrement = this.decrement.bind(this);
 this.reset = this.reset.bind(this);
 }
  reset() {
    this.setState({
      count: 0
    });
  }
  increment() {
    this.setState(state => ({
      count: state.count + 1
    }));
  }
  decrement() {
    this.setState(state => ({
      count: state.count - 1
    }));
  }
  render() {
    return (
      <div>
        <button className='inc' onClick={this.increment}>Increment!</button>
        <button className='dec' onClick={this.decrement}>Decrement!</button>
        <button className='reset' onClick={this.reset}>Reset</button>
        <h1>Current Count: {this.state.count}</h1>
      </div>
    );
  }
};