return binding.writeString(fd, buffer, offset, length, req);

enter code here

var express = require('express');
var router = express.Router();
router.get('/', function(req, res, next) {
  res.render('led', { title: 'LED Control' });
});
router.get('/:switch', function(req, res, next) {
    var onoff = req.params.switch;
    if (onoff == 'on') setLED(1);
    if (onoff == 'off') setLED(0);
    res.render('led', { title: 'LED Control : ' + req.params.switch });
});
module.exports = router;
// LED 제어 function
function setLED(flag) {
    var fs = require('fs');
    fs.open('/dev/ttyUSB0','a', 666, function(e, fd) {
        fs.write(fd, flag ? '1' : '0', null, null, null, function() {
            fs.close(fd, function() { });
        }); 
    });
}

---

Where do you fix it? OTLstrong text

return binding.writeString(fd, buffer, offset, length, req); ^

TypeError: First argument must be file descriptor at TypeError (native) at Object.fs.write (fs.js:652:18) at /home/pi/ardu/routes/led.js:23:6 at FSReqWrap.oncomplete (fs.js:82:15)

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