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id	title	challengeType	forumTopicId
5a24c314108439a4d4036142	Manage State Locally First	6	301431

Description

Here you'll finish creating the DisplayMessages component.

Instructions

First, in the render() method, have the component render an input element, button element, and ul element. When the input element changes, it should trigger a handleChange() method. Also, the input element should render the value of input that's in the component's state. The button element should trigger a submitMessage() method when it's clicked. Second, write these two methods. The handleChange() method should update the input with what the user is typing. The submitMessage() method should concatenate the current message (stored in input) to the messages array in local state, and clear the value of the input. Finally, use the ul to map over the array of messages and render it to the screen as a list of li elements.

Tests

tests:
  - text: 'The <code>DisplayMessages</code> component should initialize with a state equal to <code>{ input: "", messages: [] }</code>.'
    testString: 'assert((function() { const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages)); const initialState = mockedComponent.state(); return ( typeof initialState === ''object'' && initialState.input === '''' && initialState.messages.length === 0); })());'
  - text: The <code>DisplayMessages</code> component should render a <code>div</code> containing an <code>h2</code> element, a <code>button</code> element, a <code>ul</code> element, and <code>li</code> elements as children.
    testString: 'async () => { const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages)); const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100)); const state = () => { mockedComponent.setState({messages: [''__TEST__MESSAGE'']}); return waitForIt(() => mockedComponent )}; const updated = await state(); assert(updated.find(''div'').length === 1 && updated.find(''h2'').length === 1 && updated.find(''button'').length === 1 && updated.find(''ul'').length === 1 && updated.find(''li'').length > 0); }; '
  - text: <code>.map</code> should be used on the <code>messages</code> array.
    testString: assert(code.match(/this\.state\.messages\.map/g));
  - text: The <code>input</code> element should render the value of <code>input</code> in local state.
    testString: 'async () => { const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages)); const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100)); const causeChange = (c, v) => c.find(''input'').simulate(''change'', { target: { value: v }}); const testValue = ''__TEST__EVENT__INPUT''; const changed = () => { causeChange(mockedComponent, testValue); return waitForIt(() => mockedComponent )}; const updated = await changed(); assert(updated.find(''input'').props().value === testValue); }; '
  - text: Calling the method <code>handleChange</code> should update the <code>input</code> value in state to the current input.
    testString: 'async () => { const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages)); const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100)); const causeChange = (c, v) => c.find(''input'').simulate(''change'', { target: { value: v }}); const initialState = mockedComponent.state(); const testMessage = ''__TEST__EVENT__MESSAGE__''; const changed = () => { causeChange(mockedComponent, testMessage); return waitForIt(() => mockedComponent )}; const afterInput = await changed(); assert(initialState.input === '''' && afterInput.state().input === ''__TEST__EVENT__MESSAGE__'');  }; '
  - text: Clicking the <code>Add message</code> button should call the method <code>submitMessage</code> which should add the current <code>input</code> to the <code>messages</code> array in state.
    testString: 'async () => { const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages)); const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100)); const causeChange = (c, v) => c.find(''input'').simulate(''change'', { target: { value: v }}); const initialState = mockedComponent.state(); const testMessage_1 = ''__FIRST__MESSAGE__''; const firstChange = () => { causeChange(mockedComponent, testMessage_1); return waitForIt(() => mockedComponent )}; const firstResult = await firstChange(); const firstSubmit = () => { mockedComponent.find(''button'').simulate(''click''); return waitForIt(() => mockedComponent )}; const afterSubmit_1 = await firstSubmit(); const submitState_1 = afterSubmit_1.state(); const testMessage_2 = ''__SECOND__MESSAGE__''; const secondChange = () => { causeChange(mockedComponent, testMessage_2); return waitForIt(() => mockedComponent )}; const secondResult = await secondChange(); const secondSubmit = () => { mockedComponent.find(''button'').simulate(''click''); return waitForIt(() => mockedComponent )}; const afterSubmit_2 = await secondSubmit(); const submitState_2 = afterSubmit_2.state(); assert(initialState.messages.length === 0 && submitState_1.messages.length === 1 && submitState_2.messages.length === 2 && submitState_2.messages[1] === testMessage_2); }; '
  - text: The <code>submitMessage</code> method should clear the current input.
    testString: 'async () => { const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages)); const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100)); const causeChange = (c, v) => c.find(''input'').simulate(''change'', { target: { value: v }}); const initialState = mockedComponent.state(); const testMessage = ''__FIRST__MESSAGE__''; const firstChange = () => { causeChange(mockedComponent, testMessage); return waitForIt(() => mockedComponent )}; const firstResult = await firstChange(); const firstState = firstResult.state(); const firstSubmit = () => { mockedComponent.find(''button'').simulate(''click''); return waitForIt(() => mockedComponent )}; const afterSubmit = await firstSubmit(); const submitState = afterSubmit.state(); assert(firstState.input === testMessage && submitState.input === ''''); }; '

Challenge Seed

class DisplayMessages extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      input: '',
      messages: []
    }
  }
  // Add handleChange() and submitMessage() methods here

  render() {
    return (
      <div>
        <h2>Type in a new Message:</h2>
        { /* Render an input, button, and ul below this line */ }

        { /* Change code above this line */ }
      </div>
    );
  }
};

After Test

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

Solution

class DisplayMessages extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      input: '',
      messages: []
    }
 this.handleChange = this.handleChange.bind(this);
   this.submitMessage = this.submitMessage.bind(this);
 }
  handleChange(event) {
    this.setState({
      input: event.target.value
    });
  }
  submitMessage() {
    this.setState((state) => {
      const currentMessage = state.input;
      return {
        input: '',
        messages: state.messages.concat(currentMessage)
      };  
    });
  }
  render() {
    return (
      <div>
        <h2>Type in a new Message:</h2>
        <input
          value={this.state.input}
          onChange={this.handleChange}/><br/>
        <button onClick={this.submitMessage}>Submit</button>
        <ul>
          {this.state.messages.map( (message, idx) => {
              return (
                 <li key={idx}>{message}</li>
              )
            })
          }
        </ul>
      </div>
    );
  }
};

8.2 KiB Raw Blame History