docs: 新人培训

Author: MuYunyun

.gitignore

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+node_modules

README.md

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-# ReactHooksTraining
+Hooks 新人培训演讲大纲
+
+### React Logo 与 Hooks
+
+![](http://with.muyunyun.cn/ddbdcec2fc39ba350fc74647f4fad6f5.jpg-300)
+
+React 的 logo 是一个原子图案, 原子组成了物质。类似的, React 就如原子般构成了页面的表现; 而 Hooks 就如夸克, 其更接近 React 本质的样子, 但是直到 4 年后的今天才被真正设计出来。 —— Dan in React Conf(2018)
+
+### why Hooks?
+
+一: `多个组件间逻辑复用`: 在 Class 中使用 React 不能将带有 state 的逻辑给单独抽离成 function, 其只能通过嵌套组件的方式来解决多个组件间逻辑复用的问题, 基于嵌套组件的思想存在 [HOC](https://github.com/MuYunyun/blog/blob/master/React/从0到1实现React/8.HOC探索.md) 与 `render props` 两种设计模式。但是这两种设计模式是否存在缺陷呢?
+
+* 嵌套地狱, 当嵌套层级过多后, 数据源的追溯会变得十分困难, 导致定位 bug 不容易; (hoc、render props)
+
+![](http://with.muyunyun.cn/b9147e8bd39e7badccc3190fb473755f.jpg)
+
+* 性能, 需要额外的组件实例存在额外的开销; (hoc、render props)
+* 命名重复性, 在一个组件中同时使用多个 hoc, 不排除这些 hoc 里的方法存在命名冲突的问题; (hoc)
+
+二: `单个组件中的逻辑复用`: Class 中的生命周期 `componentDidMount`、`componentDidUpdate` 甚至 `componentWillUnMount` 中的大多数逻辑基本是类似的, 必须拆散在不同生命周期中维护相同的逻辑对使用者是不友好的, 这样也造成了组件的代码量增加。
+
+![](http://with.muyunyun.cn/0c94989b2eced65c368ff2389464fd0a.jpg-400)
+
+![](http://with.muyunyun.cn/d21d7974dbec9a49603e2211b354496c.jpg-400)
+
+三: Class 的其它一些问题: 在 React 使用 Class 需要书写大量样板, 用户通常会对 Class 中 Constructor 的 bind 以及 this 的使用感到困惑; 当结合 class 与 TypeScript 一起使用时, 需要对 defaultValue 做额外声明处理; 此外 React Team 表示 Class 在机器编译优化方面也不是很理想。
+
+### React Hooks 使用中的问题
+
+#### 闭包陷阱
+
+* demo1: 闭包陷阱1。 [Demo 地址](https://codesandbox.io/s/22y21468r)
+
+1. Hooks/class demo 对比演示;
+2. Hooks/class 互相切换为对方的形态;
+
+结论: 问题不在于是使用 Hooks 还是 class, 本质是受到闭包的影响。
+
+* demo2: 闭包陷阱2
+
+由 Class 转换过来的用户习惯 `setCount(count + 1))` 的方式。但在 Hooks 中这样子使用会产生闭包问题导致 `count` 不会增加。
+
+```js
+function Demo() {
+  const [count, setCount] = React.useState(0)
+  useEffect(() => {
+    const id = setInterval(() => {
+      setCount(count + 1)
+    }, 2000)
+
+    return () => {
+      clearInterval(id)
+    }
+  }, [])
+  return (
+    <div>Count: {count}</div>
+  )
+}
+```
+
+提供 3 种解法。用户说还是想用 `setCount(count + 1)` 的形式怎么办
+
+引出为此提供 `useInterval` 钩子, 顺利过渡到 `beast-hooks`
+
+```js
+function useInterval(callback, delay: number) {
+  const cbRef = useRef({})
+  useEffect(() => {
+    cbRef.current = callback
+  }, [callback])
+  useEffect(() => {
+    setInterval(() => {
+      cbRef.current()
+    }, delay)
+  }, [delay])
+}
+```
+
+用法:
+
+```js
+function Demo() {
+  const [count, setCount] = React.useState(0)
+
+  useInterval(() => {
+    setCount(count + 1)
+  }, 2000)
+
+  return (<div>Count: {count}</div>)
+}
+```
+
+### React Hooks 内部探究
+
+以 `useState` 和 `useReducer` 为例
+
+#### 使用 useState 实现 useReducer
+
+```js
+import * as React from 'react'
+const { useState, useRef, useCallback } = React
+
+function useReducer(reducer, initialState) {
+  const [state, setState] = useState(initialState)
+  const reducerRef = useRef(reducer)
+  const stateRef = useRef(state)
+
+  const dispatch = useCallback((action) => {
+    setState(reducerRef.current(stateRef.current, action))
+  }, [])
+
+  useEffect(() => {
+    reducerRef.current = reducer
+  }, [reducer])
+
+  useEffect(() => {
+    stateRef.current = state
+  }, [state])
+
+  return [state, dispatch]
+}
+```
+
+#### 使用 useReducer 实现 useState
+
+```js
+import * as React from 'react'
+const { useReducer, useCallback } = React
+
+function useState(initialState) {
+  const [state, dispatch] = useReducer((state, action) => {
+    return action
+  }, initialState)
+
+  const setState = useCallback(
+    (newState) => dispatch(newState), []
+  )
+
+  return [state, setState]
+}
+```
+
+### 相关链接
+
+* [React Hooks 深入系列](https://github.com/MuYunyun/blog/blob/master/React/React_Hooks深入系列.md)
+* [React Hooks 设计模式](https://github.com/MuYunyun/blog/blob/master/React/React_Hooks设计模式.md)

package.json

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+{
+  "name": "new",
+  "version": "1.0.0",
+  "description": "",
+  "keywords": [],
+  "main": "src/index.js",
+  "dependencies": {
+    "react": "16.8.6",
+    "react-dom": "16.8.6",
+    "react-scripts": "2.1.8"
+  },
+  "devDependencies": {
+    "typescript": "3.3.3"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  },
+  "browserslist": [
+    ">0.2%",
+    "not dead",
+    "not ie <= 11",
+    "not op_mini all"
+  ]
+}

public/index.html

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+<!DOCTYPE html>
+<html lang="en">
+
+<head>
+	<meta charset="utf-8">
+	<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
+	<meta name="theme-color" content="#000000">
+	<!--
+      manifest.json provides metadata used when your web app is added to the
+      homescreen on Android. See https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/
+    -->
+	<link rel="manifest" href="%PUBLIC_URL%/manifest.json">
+	<link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
+	<!--
+      Notice the use of %PUBLIC_URL% in the tags above.
+      It will be replaced with the URL of the `public` folder during the build.
+      Only files inside the `public` folder can be referenced from the HTML.
+
+      Unlike "/favicon.ico" or "favicon.ico", "%PUBLIC_URL%/favicon.ico" will
+      work correctly both with client-side routing and a non-root public URL.
+      Learn how to configure a non-root public URL by running `npm run build`.
+    -->
+	<title>React App</title>
+</head>
+
+<body>
+	<noscript>
+		You need to enable JavaScript to run this app.
+	</noscript>
+	<div id="root"></div>
+	<!--
+      This HTML file is a template.
+      If you open it directly in the browser, you will see an empty page.
+
+      You can add webfonts, meta tags, or analytics to this file.
+      The build step will place the bundled scripts into the <body> tag.
+
+      To begin the development, run `npm start` or `yarn start`.
+      To create a production bundle, use `npm run build` or `yarn build`.
+    -->
+</body>
+
+</html>

src/index.js

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+import React, { useState, useRef, useEffect, useReducer } from "react"
+import ReactDOM from "react-dom"
+import useInterval from './useInterval'
+
+import "./styles.css"
+
+function HookApp() {
+  const [count, setCount] = useState(0)
+  const handleAdd = () => {
+    setCount(count + 1)
+  }
+  const handleAlert = () => {
+    setTimeout(() => {
+      window.alert(count)
+    }, 2000)
+  }
+  return (
+    <div className="App">
+      <h1>Hook</h1>
+      <h1>{count}</h1>
+      <button onClick={handleAdd}>add</button>
+      <button onClick={handleAlert}>alert</button>
+    </div>
+  )
+}
+
+class ClassApp extends React.Component {
+  state = {
+    count: 0
+  };
+
+  handleAdd = () => {
+    this.setState({
+      count: this.state.count + 1
+    });
+  };
+
+  handleAlert = () => {
+    setTimeout(() => {
+      window.alert(this.state.count);
+    }, 2000);
+  };
+
+  render() {
+    return (
+      <div className="App">
+        <h1>Class</h1>
+        <h1>{this.state.count}</h1>
+        <button onClick={this.handleAdd}>add</button>
+        <button onClick={this.handleAlert}>alert</button>
+      </div>
+    );
+  }
+}
+
+/* --------------- 分割线 --------------- */
+
+function Demo() {
+  const [count, setCount] = React.useState(0)
+
+  useEffect(() => {
+    const id = setInterval(() => {
+      setCount(count + 1)
+    }, 2000)
+
+    return () => {
+      clearInterval(id)
+    }
+  }, [])
+
+  return <div>Count: {count}</div>
+}
+
+function View() {
+  return (
+    <React.Fragment>
+      <HookApp />
+      <hr />
+      <ClassApp />
+      <hr />
+      {/* <Demo /> */}
+    </React.Fragment>
+  );
+}
+
+const rootElement = document.getElementById("root");
+ReactDOM.render(<View />, rootElement);

src/styles.css

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+.App {
+  font-family: sans-serif;
+  text-align: center;
+}
+
+button {
+  padding: 10px 20px;
+  margin: 10px;
+}

src/useInterval.js

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+import React, { useState, useRef, useEffect } from "react"
+
+export default function useInterval(callback, delay) {
+  const cbRef = useRef({})
+  useEffect(() => {
+    cbRef.current = callback
+  }, [callback])
+  useEffect(() => {
+    const id = setInterval(() => {
+      cbRef.current()
+    }, delay)
+
+    return () => clearInterval(id)
+  }, [delay])
+}