261 lines
7.4 KiB
Markdown
261 lines
7.4 KiB
Markdown
---
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id: 5a24c314108439a4d4036142
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title: 首先在本地管理状态
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challengeType: 6
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forumTopicId: 301431
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dashedName: manage-state-locally-first
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---
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# --description--
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这一关的任务是完成 `DisplayMessages` 组件的创建。
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# --instructions--
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首先，在 `render()` 方法中，让组件渲染 `input`、`button`、`ul` 三个元素。 `input` 元素的改变会触发 `handleChange()` 方法。 此外，`input` 元素会渲染组件状态中 `input` 的值。 点击按钮 `button` 需触发 `submitMessage()` 方法。
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接着，写出这两种方法。 `handleChange()` 方法会更新 `input` 为用户正在输入的内容。 `submitMessage()` 方法把当前存储在 `input` 的消息与本地状态的 `messages` 数组连接起来，并清除 `input` 的值。
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最后，在 `ul` 中展示 `messages` 数组，其中每个元素内容需放到 `li` 元素内。
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# --hints--
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`DisplayMessages` 组件的初始状态应是 `{ input: "", messages: [] }`。
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```js
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assert(
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(function () {
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const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
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const initialState = mockedComponent.state();
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return (
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typeof initialState === 'object' &&
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initialState.input === '' &&
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initialState.messages.length === 0
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);
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})()
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);
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```
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`DisplayMessages` 组件应渲染含 `h2`、`button`、`ul`、`li` 四个子元素的`div`
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```js
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async () => {
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const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
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const waitForIt = (fn) =>
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new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
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const state = () => {
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mockedComponent.setState({ messages: ['__TEST__MESSAGE'] });
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return waitForIt(() => mockedComponent);
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};
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const updated = await state();
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assert(
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updated.find('div').length === 1 &&
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updated.find('h2').length === 1 &&
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updated.find('button').length === 1 &&
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updated.find('ul').length === 1 &&
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updated.find('li').length > 0
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);
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};
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```
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`.map` 应该用于 `messages` 数组。
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```js
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assert(code.match(/this\.state\.messages\.map/g));
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```
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`input` 元素应渲染本地状态中的 `input` 值。
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```js
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async () => {
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const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
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const waitForIt = (fn) =>
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new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
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const causeChange = (c, v) =>
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c.find('input').simulate('change', { target: { value: v } });
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const testValue = '__TEST__EVENT__INPUT';
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const changed = () => {
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causeChange(mockedComponent, testValue);
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return waitForIt(() => mockedComponent);
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};
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const updated = await changed();
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assert(updated.find('input').props().value === testValue);
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};
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```
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调用 `handleChange` 方法时应更新状态中的 `input` 值为当前输入。
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```js
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async () => {
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const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
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const waitForIt = (fn) =>
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new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
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const causeChange = (c, v) =>
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c.find('input').simulate('change', { target: { value: v } });
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const initialState = mockedComponent.state();
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const testMessage = '__TEST__EVENT__MESSAGE__';
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const changed = () => {
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causeChange(mockedComponent, testMessage);
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return waitForIt(() => mockedComponent);
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};
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const afterInput = await changed();
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assert(
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initialState.input === '' &&
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afterInput.state().input === '__TEST__EVENT__MESSAGE__'
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);
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};
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```
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单击 `Add message` 按钮应调用 `submitMessage` 方法，添加当前 `input` 到状态中的 `messages` 数组。
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```js
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async () => {
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const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
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const waitForIt = (fn) =>
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new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
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const causeChange = (c, v) =>
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c.find('input').simulate('change', { target: { value: v } });
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const initialState = mockedComponent.state();
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const testMessage_1 = '__FIRST__MESSAGE__';
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const firstChange = () => {
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causeChange(mockedComponent, testMessage_1);
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return waitForIt(() => mockedComponent);
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};
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const firstResult = await firstChange();
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const firstSubmit = () => {
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mockedComponent.find('button').simulate('click');
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return waitForIt(() => mockedComponent);
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};
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const afterSubmit_1 = await firstSubmit();
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const submitState_1 = afterSubmit_1.state();
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const testMessage_2 = '__SECOND__MESSAGE__';
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const secondChange = () => {
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causeChange(mockedComponent, testMessage_2);
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return waitForIt(() => mockedComponent);
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};
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const secondResult = await secondChange();
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const secondSubmit = () => {
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mockedComponent.find('button').simulate('click');
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return waitForIt(() => mockedComponent);
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};
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const afterSubmit_2 = await secondSubmit();
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const submitState_2 = afterSubmit_2.state();
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assert(
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initialState.messages.length === 0 &&
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submitState_1.messages.length === 1 &&
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submitState_2.messages.length === 2 &&
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submitState_2.messages[1] === testMessage_2
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);
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};
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```
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`submitMessage` 方法应清除当前输入。
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```js
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async () => {
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const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
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const waitForIt = (fn) =>
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new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
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const causeChange = (c, v) =>
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c.find('input').simulate('change', { target: { value: v } });
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const initialState = mockedComponent.state();
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const testMessage = '__FIRST__MESSAGE__';
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const firstChange = () => {
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causeChange(mockedComponent, testMessage);
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return waitForIt(() => mockedComponent);
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};
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const firstResult = await firstChange();
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const firstState = firstResult.state();
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const firstSubmit = () => {
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mockedComponent.find('button').simulate('click');
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return waitForIt(() => mockedComponent);
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};
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const afterSubmit = await firstSubmit();
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const submitState = afterSubmit.state();
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assert(firstState.input === testMessage && submitState.input === '');
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};
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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(<DisplayMessages />, document.getElementById('root'))
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```
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## --seed-contents--
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```jsx
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class DisplayMessages 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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input: '',
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messages: []
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}
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}
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// Add handleChange() and submitMessage() methods here
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render() {
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return (
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<div>
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<h2>Type in a new Message:</h2>
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{ /* Render an input, button, and ul 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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```
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# --solutions--
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```jsx
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class DisplayMessages 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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input: '',
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messages: []
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}
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this.handleChange = this.handleChange.bind(this);
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this.submitMessage = this.submitMessage.bind(this);
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}
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handleChange(event) {
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this.setState({
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input: event.target.value
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});
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}
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submitMessage() {
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this.setState((state) => {
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const currentMessage = state.input;
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return {
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input: '',
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messages: state.messages.concat(currentMessage)
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};
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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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<h2>Type in a new Message:</h2>
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<input
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value={this.state.input}
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onChange={this.handleChange}/><br/>
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<button onClick={this.submitMessage}>Submit</button>
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<ul>
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{this.state.messages.map( (message, idx) => {
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return (
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<li key={idx}>{message}</li>
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)
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})
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}
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</ul>
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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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