freeCodeCamp/curriculum/challenges/chinese-traditional/03-front-end-development-libraries/react-and-redux/manage-state-locally-first.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
5a24c314108439a4d4036142	首先在本地管理狀態	6	301431	manage-state-locally-first

--description--

這一關的任務是完成 DisplayMessages 組件的創建。

--instructions--

首先，在 render() 方法中，讓組件渲染 input、button、ul 三個元素。 input 元素的改變會觸發 handleChange() 方法。 此外，input 元素會渲染組件狀態中 input 的值。 點擊按鈕 button 需觸發 submitMessage() 方法。

接着，寫出這兩種方法。 handleChange() 方法會更新 input 爲用戶正在輸入的內容。 submitMessage() 方法把當前存儲在 input 的消息與本地狀態的 messages 數組連接起來，並清除 input 的值。

最後，在 ul 中展示 messages 數組，其中每個元素內容需放到 li 元素內。

--hints--

DisplayMessages 組件的初始狀態應是 { input: "", messages: [] }。

assert(
  (function () {
    const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
    const initialState = mockedComponent.state();
    return (
      typeof initialState === 'object' &&
      initialState.input === '' &&
      initialState.messages.length === 0
    );
  })()
);

DisplayMessages 組件應渲染含 h2、button、ul、li 四個子元素的div

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
  );
};

.map 應該用於 messages 數組。

assert(code.match(/this\.state\.messages\.map/g));

input 元素應渲染本地狀態中的 input 值。

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);
};

調用 handleChange 方法時應更新狀態中的 input 值爲當前輸入。

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__'
  );
};

單擊 Add message 按鈕應調用 submitMessage 方法，添加當前 input 到狀態中的 messages 數組。

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
  );
};

submitMessage 方法應清除當前輸入。

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 === '');
};

--seed--

--after-user-code--

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

--seed-contents--

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>
    );
  }
};

--solutions--

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>
    );
  }
};