sertup中使用provide和inject实现组件之间的传值```js``` const username = in

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <script src="https://unpkg.com/vue@next"></script>
  </head>
  <body>
    <div id="root"></div>
  </body>
  <script>
    const app = Vue.createApp({
      // setup
      setup() {
        const { provide } = Vue;
        provide("username", "zhangsan");
        return {};
      },
      // 模板
      template: `
        <child />
        `,
    });

    // 定义全局同步子组件，接收传值，并使用
    app.component("child", {
      setup() {
        const { inject } = Vue;
        // 定义一个变量，里面的值是接收父组件传过来的
        const username = inject("username", "lisi");
        return { username };
      },
      template: `
        <h1>{{username}}</h1>
        
        `,
    });
    const vm = app.mount("#root");
  </script>
</html>