> For the complete documentation index, see [llms.txt](https://yangsx95.gitbook.io/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://yangsx95.gitbook.io/notes/front-end/react.md).

# React

* 英文官网：[React – A JavaScript library for building user interfaces (reactjs.org)](https://reactjs.org/)
* 中文官网：[React 官方中文文档 – 用于构建用户界面的 JavaScript 库 (reactjs.org)](https://zh-hans.reactjs.org/)
* Github：[facebook/react: A declarative, efficient, and flexible JavaScript library for building user interfaces. (github.com)](https://github.com/facebook/react)

由Facebook开源的用于动态构建用户界面的 JavaScript 库(只关注于视图)。

## 特点

1. 声明式编码
2. 组件化编码
3. React Native 编写原生应用
4. 高效
   1. 使用虚拟DOM，不总直接操作真实DOM
   2. DOM Diffing算法，最小页面重绘

## 安装React

1. `react.js`：React核心库。
2. `react-dom.js`：提供操作DOM的react扩展库。
3. `babel.min.js`：解析JSX语法代码转为JS代码的库。

## Hello World

### 非JSX方式

```html
<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
<div id="app"></div>

<script src="https://unpkg.com/react@17/umd/react.development.js" crossorigin></script>
<script src="https://unpkg.com/react-dom@17/umd/react-dom.development.js" crossorigin></script>
<script type="text/javascript">
    // 创建虚拟dom
    const vdom = React.createElement("h1", {id: "title"}, "Hello World");
    // 渲染虚拟dom到页面指定的div中
    ReactDOM.render(vdom, document.getElementById('app'));
</script>
</body>
</html>
```

### JSX方式

```html
<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
<div id="app"></div>

<script src="https://unpkg.com/react@17/umd/react.development.js" crossorigin></script>
<script src="https://unpkg.com/react-dom@17/umd/react-dom.development.js" crossorigin></script>
<script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>
<script type="text/babel">
    // 创建虚拟dom
    const vdom = (
        <h1 id="title">Hello World</h1>
    );
    // 渲染虚拟dom到页面指定的div中
    ReactDOM.render(vdom, document.getElementById('app'));
</script>
</body>
</html>
```
