Callbacks and Serial Port Draining in Node.js

Question

I have a function that, when you press a key, sends a keycode over a serial port. However, in this circumstance, onKey 's callback is getting activated faster than the data can be written to the serial port, so I need to use a drain function which sends all data and calls back when it's done.

How do I wait for the drainSerialPort callback to execute before attempting to send the next key code? I assume there's a better way to structure the three functions.

onKey(function(key) {
  writeSerial(key, function() {
    drainSerialPort(function() {
      // Wait for this callback to be called to continue
    });
  });
});

Answer 1

According to your requirement the best option for you is asynchronus. First your function onKey is executed, after when it completed function writeSerial is executed.

        var onKey = function (key) {
        };
async.eachSeries(onKey, writeSerial, function (err) {
    if (err) {
        res.json({status: 0, msg: "OOPS! How is this possible?"});
    }
    drainSerialPort(function () {
        // Wait for this callback to be called to continue
    });
    res.json("Series Processing Done");
})
var writeSerial = function (key) {
};