getting syntax error

[stoneobscurity]

root@vmUniFi:/home/stone/node_modules/unifi2mqtt# unifi2mqtt -a 127.0.0.1 -p 8443 -c username -s sekret -w obscurity -k -u mqtt://username:[email protected]:1883 /usr/local/lib/node_modules/unifi2mqtt/index.js:16 let mqttConnected; ^^^

SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode at exports.runInThisContext (vm.js:53:16) at Module._compile (module.js:374:25) at Object.Module._extensions..js (module.js:417:10) at Module.load (module.js:344:32) at Function.Module._load (module.js:301:12) at Function.Module.runMain (module.js:442:10) at startup (node.js:136:18) at node.js:966:3