bootstrap-vue/src/mixins/listen-on-root.js

Quickly integrate Bootstrap 4 components with Vue.js

import { isArray } from '../utils/array'
/**
 * Issue #569: collapse::toggle::state triggered too many times
 * @link https://github.com/bootstrap-vue/bootstrap-vue/issues/569
 */

const BVRL = '__BV_root_listeners__'

export default {
  methods: {
    /**
         * Safely register event listeners on the root Vue node.
         * While Vue automatically removes listeners for individual components,
         * when a component registers a listener on root and is destroyed,
         * this orphans a callback because the node is gone,
         * but the root does not clear the callback.
         *
         * This adds a non-reactive prop to a vm on the fly
         * in order to avoid object observation and its performance costs
         * to something that needs no reactivity.
         * It should be highly unlikely there are any naming collisions.
         * @param {string} event
         * @param {function} callback
         * @chainable
         */
    listenOnRoot (event, callback) {
      if (!this[BVRL] || !isArray(this[BVRL])) {
        this[BVRL] = []
      }
      this[BVRL].push({ event, callback })
      this.$root.$on(event, callback)
      return this
    },

    /**
         * Convenience method for calling vm.$emit on vm.$root.
         * @param {string} event
         * @param {*} args
         * @chainable
         */
    emitOnRoot (event, ...args) {
      this.$root.$emit(event, ...args)
      return this
    }
  },

  beforeDestroy () {
    if (this[BVRL] && isArray(this[BVRL])) {
      while (this[BVRL].length > 0) {
        // shift to process in order
        const { event, callback } = this[BVRL].shift()
        this.$root.$off(event, callback)
      }
    }
  }
}