connect之后输出mqtt实例

{
    connected: true,
    disconnecting: false,
    //...
}

end(true)断开之后输出mqtt实例

{
    connected: true,
    disconnected: true,
    disconnecting: true,
    //...
}

得到结果

//连接了 
this.client != null && (this.client.connected==true && this.client.disconnecting==false && (this.client.disconnected==undefined || this.client.disconnected==false))
//未连接 
this.client == null || (this.client.connected==false || (this.client.disconnected==true && this.client.disconnecting==true))