using Node.js, what is the best way to write to a file several times a second

Question

I am new to Node.js. I have a file on my file system that controls some kind of output on my hardware. Content of the file could be an integer between 0 to 100.

I want to write to this file with a fixed delay (say every 100ms). So I wrode this code:

var duty_percentfile = fs.openSync("/sys/class/pwm/ehrpwm.1:0/duty_percent", "w");

var fade = function(){
    fs.writeSync(duty_percentfile, i, null);
    i = i + 5;
}

setInterval(fade, 100);

First of all, is this the best way?

Secondly, I am getting this error dispute the fact it accomplishes the job:

fs.js:321


return binding.write(fd, buffer, offset, length, position);
                 ^
Error: EINVAL, invalid argument
    at Object.writeSync (fs.js:321:18)
    at Timer.<anonymous> (/var/lib/cloud9/myApps/test.js:22:8)
    at Timer.ontimeout (timers.js:223:14)

Answer 1

I found the answer here: https://github.com/isaacs/node-graceful-fs/issues/6

It is a known issue that is fixed in node 0.6.15 about 22 days ago. Time to upgrade I guess!

Answer 2

Instead of null you should specify 0 as a position (if that's what you want). Also your i is not initialized and will not increment.

Try this instead:

var duty_percentfile = fs.openSync("/sys/class/pwm/ehrpwm.1:0/duty_percent", "w")
  , value = 0 // or whatever your initial value is
;

setInterval(function(){
  fs.writeSync(duty_percentfile, value, 0);
  value += 5;
}, 100);