（六）单文件应用

cosnt app = Vue.createApp({})
app.component('组件名字', {
    data() {
        return {
            content: ''
        }
    },

    computed: {
        return this.content.length
    },

    template: `
        <div>
            <input v-model="content" />
            <p>你共输入了 {{ count }} 个字符</p>
        </div>
    `
})

const vm = app.mount('#app')

cosnt app = Vue.createApp({})

app.component('全局组件名字', {
    template: `
    <div>
        <h1>字符统计应用</h1>
        <WordCount />
    </div>`
})

const vm = app.mount('#app')

// 先引入组件 
import ComponentApp from './component/index.vue'

const app = Vue.createApp({
    // 注册组件
    components: {
        ComponentApp
    }
})

const vm = app.mount({#app})