Vue.extend和VueComponent的关系源码解析

import Vue from 'vue'
let VueComponent = Vue.extend({})
VueComponent.prototype.__proto__ == Vue.prototype	// true

import Vue from 'vue/dist/vue.esm.js'   // 必须引入这个版本的Vue才可以使用template选项
new Vue({
    el: "#app",
    template: `
        <App></App>
    `,
    components: { App },
    mounted() {
        let app = this.$children[0];        // App组件实例
        let VueComponent = app.constructor  // App构造函数
        console.log(app);
        console.log(VueComponent);
        console.log(VueComponent.prototype.__proto__ == Vue.prototype);
    }
})

Vue.component("Toast", {})              // 全局注册组件
console.log(Vue.component("Toast"));    // Toast组件构造函数

let VueComponent = Vue.extend({})
new VueComponent({
    el: "#app",
    template: `<h1>Vue.extend的使用</h1>`
})

<template>
  <h1 class="title" v-if="show">{{ title }}</h1>
</template>
<script>
  export default {
    name: "my-toast",
    props: {
      title: {
        typeof: String,
        default: ""
      }
    },
    data() {
      return {
        show: true
      };
    },
    created() {
      setTimeout(() => {
        this.show = false;
        this.$nextTick(() => {
          this.$destroy();
        });
      }, 2000);
    }
  };
</script>
<style>
  .title {
    width: 180px;
    height: 50px;
    position: fixed;
    right: 20px;
    top: 20px;
    background-color: rgba(0, 0, 0, 0.15);
    text-align: center;
    line-height: 50px;
    border-radius: 8px;
    font-size: 16px;
  }
</style>

import Vue from 'vue';
import myToast from './components/my-toast.vue';
Vue.prototype.$toast = function (title) {
    const ToastComponent = Vue.extend(myToast);
    const toastComponent = new ToastComponent({
        propsData: {
            title
        }
    })
    toastComponent.$mount(document.createElement('div'));
    document.body.appendChild(toastComponent.$el);
}

// ....某vue页面  
mounted() {
    this.$toast("测试");
}

Vue.extend = function (extendOptions: any): typeof Component {
    extendOptions = extendOptions || {}
    // this指的是Vue
    const Super = this
    // 每个组件构造函数都有唯一的cid
    const SuperId = Super.cid
    // 创建完的VueComponent构造函数，会保存到_Ctor中
    // 如果下次传入相同的extendOptions和SuperId，就直接取用缓存内的值
    const cachedCtors = extendOptions._Ctor || (extendOptions._Ctor = {})
    if (cachedCtors[SuperId]) {
      return cachedCtors[SuperId]
    }
    // 获取组件name
    const name =
      getComponentName(extendOptions) || getComponentName(Super.options)
    if (__DEV__ && name) {
        // 校验组件name
      validateComponentName(name)
    }
    // 创建VueComponent构造函数
    const Sub = function VueComponent(this: any, options: any) {
      this._init(options)
    } as unknown as typeof Component
    // 重点：实现了原型链继承，让VueComponent的原型指向Vue的原型
    // Vue的原型的所有方法和属性，在VueComponent也存在
    Sub.prototype = Object.create(Super.prototype)
    Sub.prototype.constructor = Sub
    // 生成唯一cid
    Sub.cid = cid++
    // 传入的extendOptions和Vue.options合并
    Sub.options = mergeOptions(Super.options, extendOptions)
    Sub['super'] = Super
    // 配置props的响应式
    if (Sub.options.props) {
      initProps(Sub)
    }
    // 配置computed的响应式
    if (Sub.options.computed) {
      initComputed(Sub)
    }
    // 继承静态方法
    Sub.extend = Super.extend
    Sub.mixin = Super.mixin
    Sub.use = Super.use
    //  ASSET_TYPES = ['component', 'directive', 'filter']
    ASSET_TYPES.forEach(function (type) {
      Sub[type] = Super[type]
    })
    if (name) {
      Sub.options.components[name] = Sub
    }
    // 保存基础配置
    Sub.superOptions = Super.options
    Sub.extendOptions = extendOptions
    Sub.sealedOptions = extend({}, Sub.options)
    // 设置缓存
    cachedCtors[SuperId] = Sub
    return Sub
  }

// 继承原型
Sub.prototype = Object.create(Super.prototype)
Sub.prototype.constructor = Sub
// 继承静态方属性和方法
// 继承静态方法
Sub.extend = Super.extend
Sub.mixin = Super.mixin
Sub.use = Super.use
//  ASSET_TYPES = ['component', 'directive', 'filter']
ASSET_TYPES.forEach(function (type) {
    Sub[type] = Super[type]
})