use of instead of in

server.js

@@ -17,7 +17,7 @@ export function recv(callback, errorCallback) {
       console.log('connection recieved: ' +
         con.remoteAddress + ":" + con.remotePort);
       let data = [];
-      for (let key in Object.keys(functions)) {
+      for (let key of Object.keys(functions)) {
         data.push({ n: key, a: reqs[key] })
       }
       let functions_str = JSON.stringify(data);