Uncaught (in promise) TypeError: Assignment to constant variable.

问题：Uncaught (in promise) TypeError: Assignment to constant variable.

WS._startWebSocket = function (projectId,viewType,userId) {

        // 连接选项
        const options = {
            connectTimeout: 4000, // 超时时间
            // 认证信息
            clientId: 'client_'+projectId+"_"+viewType+"_"+userId,
            username: 'gfkd',
            password: '123456',
        }

        client = mqtt.connect('ws://192.168.43.141:8083/mqtt', options)

原因： const定义了变量且存在初始值。 下面又给tableJoin赋值，则报错了

解决：const 改为 let