Detailed explanation of Vue's self-implementation of dispatch and broadcast (dispatch and broadcast)

function broadcast(componentName, eventName, params) {
 this.$children.forEach(child => {
  const name = child.$options.name;

  if (name === componentName) {
   child.$emit.apply(child, [eventName].concat(params));
  } else {
   // todo If params is an empty array, it will receive undefined
   broadcast.apply(child, [componentName, eventName].concat([params]));
  }
 });
}
export default {
 methods: {
  dispatch(componentName, eventName, params) {
   let parent = this.$parent || this.$root;
   let name = parent.$options.name;

   while (parent && (!name || name !== componentName)) {
    parent = parent.$parent;

    if (parent) {
     name = parent.$options.name;
    }
   }
   if (parent) {
    parent.$emit.apply(parent, [eventName].concat(params));
   }
  },
  broadcast(componentName, eventName, params) {
   broadcast.call(this, componentName, eventName, params);
  }
 }
};

<template>
 <div>
  <h1>I am the parent component</h1>
  <button @click="handleClick">Trigger event</button> <child />
 </div>
</template>
<script>
import Emitter from "@/mixins/emitter.js";
import Child from "./child";
export default {
 name: "componentA",
 mixins: [Emitter],
 created() {
  this.$on("child-to-p", this.handleChild);
 },
 methods: {
  handleClick() {
   this.broadcast("componentB", "on-message", "Hello Vue.js");
  },
  handleChild(val) {
   alert(val);
  }
 },
 components:
  Child
 }
};
</script>

<template>
 <div>I am a child component</div>
</template>
<script>
import Emitter from "@/mixins/emitter.js";
export default {
 name: "componentB",
 mixins: [Emitter],
 created() {
  this.$on("on-message", this.showMessage);
  this.dispatch("componentA", "child-to-p", "hello parent");
 },
 methods: {
  showMessage(text) {
   window.alert(text);
  }
 }
};
</script>