自定义Eventbus 发布订阅模式

const EventList = {};

const on = function(eventName, callback) {
  if (!EventList[eventName]) {
    EventList[eventName] = [];
  }

  EventList[eventName].push(callback);
}

const emit = function(eventName, params) {
  if (!EventList[eventName]) return;

  EventList[eventName].map((cb) => {
    cb(params);
  })
}

const off = function(eventName, callback) {
  if (!EventList[eventName]) return;

  if (callback) {
    let index = EventList[eventName].indexOf(callback);

    EventList[eventName].splice(index, 1);
  } else {
    EventList[eventName] = [];
  }
}

export default {
  $on: on,
  $emit: emit,
  $off: off
}