Function eventsAPI

02.Components/Part-2/js/vue.js:9232–9421

(Vue)

  }

  function eventsAPI (Vue) {
    /**
     * Listen on the given `event` with `fn`.
     *
     * @param {String} event
     * @param {Function} fn
     */

    Vue.prototype.$on = function (event, fn) {
      (this._events[event] || (this._events[event] = [])).push(fn);
      modifyListenerCount(this, event, 1);
      return this;
    };

    /**
     * Adds an `event` listener that will be invoked a single
     * time then automatically removed.
     *
     * @param {String} event
     * @param {Function} fn
     */

    Vue.prototype.$once = function (event, fn) {
      var self = this;
      function on() {
        self.$off(event, on);
        fn.apply(this, arguments);
      }
      on.fn = fn;
      this.$on(event, on);
      return this;
    };

    /**
     * Remove the given callback for `event` or all
     * registered callbacks.
     *
     * @param {String} event
     * @param {Function} fn
     */

    Vue.prototype.$off = function (event, fn) {
      var cbs;
      // all
      if (!arguments.length) {
        if (this.$parent) {
          for (event in this._events) {
            cbs = this._events[event];
            if (cbs) {
              modifyListenerCount(this, event, -cbs.length);
            }
          }
        }
        this._events = {};
        return this;
      }
      // specific event
      cbs = this._events[event];