Contents:

• What is react?
• React element
• React component
• render()

• React is a Javascript library
• High performance frontend framework
• Use small and isolated pieces of UI code called “components”

Initialize React App

npx create-react-app my-app
cd my-app
npm start

App structure

• manifest.json 指定了开始页面

• index.html，一切都从这里开始，这个是代码执行的源头。

• src/index.js 是一个入口文件

React.Component

class ShoppingList extends React.Component {
    render(){
        return(
            //...
        )
    }
}

React element

• React UI的最小单元
• 不可变：当元素被创建之后，你是无法改变其内容或属性的
• 可以被render进react DOM，并由其来管理

render()

• A method that returns a description of what you want to see on the screen
  • The description is called a react element
  • React display the view using the react elements returned

将React元素render到DOM root

const element = <h1>Hello, world!</h1>;
ReactDOM.render(
    element,
    document.getElementById('example')
);

function封装react element

// function that return JSX.element
function Clock(props) {
  return (
    <div>
      <h1>Hello, world!</h1>
      <h2>现在是 {props.date.toLocaleTimeString()}.</h2>
    </div>
  );
}

// function that renders element
function tick() {
  ReactDOM.render(
    <Clock date={new Date()} />,
    document.getElementById('example')
  );
}

// repeatedly calling the rendering function -- 每秒钟调用一次
setInterval(tick, 1000);

Component封装element

React.component

class Clock extends React.Component {
    render(){
        return(
           ...
           <h2>现在是 {this.props.date.toLocaleTimeString()}.</h2>
           ... 
        )
    }
}

function tick() {
...
}

setInterval(tick, 1000);

• ShoppingList: React component class
• Responsibility:
  • A component takes in parameters, called props 
  • Returns a hierarchy of views
  • Display via the render method