nodejs: http listen interferes with serialport reads

_x000D_ _x000D_ I'm trying to read in data from an arduino using serialport, and serve it to a web browser. Without the webserver (ie. if I just leave out that 'listen' call at the end), the serial data gets constantly streamed in with the expected 5 updates per second shown in the console. But when I add the 'listen' call, nothing is shown on the console until I make a request to the server with my web browser, at which time the console gets at most only one log entry added (but sometimes still nothing). The data shown in the web browser is the 'old' data from whenever the last request was made, not the current latest data from the arduino. In other words, the serial data is processed a little after each http request is served - not very useful. const http = require('http'); const serialport = require('serialport'); var serial = new serialport('/dev/ttyUSB0', { baudRate: 115200 }); var jsonStr = ''; var jsonObj = {}; function handleData(data) { jsonStr += data; if ( data.indexOf('}') > -1 ) { try { jsonObj = JSON.parse(jsonStr); console.log(jsonObj); } catch(e) {} jsonStr = ''; } }; serial.on('data', function (data) { handleData(data); }); const app = http.createServer((request, response) => { response.writeHead(200, {"Content-Type": "text/html"}); response.write(JSON.stringify(jsonObj)); response.end(); }); app.listen(3000); (The data coming from the arduino is already a JSON string which is why I'm looking for a '}' to start parsing it.) I also tried using the 'readable' event for getting the serial data but it makes no difference: serial.on('readable', function () { handleData(serial.read()); }); If I understand it correctly, the listen call itself is not blocking, it merely registers an event listener/callback to be triggered later. As an accepted answer in a related question says: "Think of server.listen(port) as being kinda similar to someElement.addEventListener('click', handler) in the browser." If node.js is single threaded then why does server.listen() return? So why is that 'listen' preventing the serial connection from receiving anything, except for briefly each time a request is served? Is there no way I can use these two features without them interfering with each other?