vue2.js

import Vue from "vue"

Vue.prototype.$events = new Vue

new Vue({})

export default {
  name: "cmp1",
  mounted() {
    this.$events.$emit("cmp1Loaded")
  }
}

export default {
  name: "cmp2",
  mounted() {
    this.$events.$once("cmp1Loaded", () => {
      console.log("cm1 component has been loaded!")
    })
  }
}