once (event, callback) {
    if (!event || !callback || !this.player) {
      showErrorMsg(this.pluginName, 'plugin.once(event, callback)')
      return
    }
    if (typeof event === 'string') {
      this.__onceEvents[event] = callback
      this.player.once(event, callback)
    } else if (Array.isArray(event)) {
      event.forEach((item) => {
        this.__onceEvents[item] = callback
        this.player.once(event, callback)
      })
    }
  }
@param { string } event
@param { Function } callback
@returns