How to write to a file in a Big loop using Javascript

Question

My code is

for (let indexM = 0; indexM < 0.5; indexM += 0.01) {
  //C
  for (let indexC = -10; indexC < 10; indexC += 0.05) {
    //X
    for (let indexX = 0; indexX < X.length; indexX++) {
      //Y = M * X[i] + C
      PredictedY = indexM * X[indexX] + indexC;
      Error += (PredictedY - Y[indexX]) * (PredictedY - Y[indexX]);
    }
    newMeanSquareError = Error / X.length;

    let M = indexM.toFixed(2);
    let C = indexC.toFixed(2);
    let MSE = newMeanSquareError.toFixed(2);

    // var data = `M slope: ${M} ` + `  Y-intercept: ${C} ` + `  MSE: ${MSE} ` + "\r\n";

    fs.writeFile(
      "HouseSales.txt",
      `M Slope : ${M}  C Intercept : ${C} MSE : ${MSE}`,
      (err) => {
        // In case of a error throw err.
        if (err) throw err;
      }
    );

    if (least > newMeanSquareError) {
      least = newMeanSquareError;
      newC = indexC;
      newM = indexM;
    }
    Error = 0;
  }
}

I am getting this error


[Error: EMFILE: too many open files, open 'F:\Semester 5\Introductiob to AI\Lab1\HouseSales.txt'] {
  errno: -4066,
  code: 'EMFILE',
  syscall: 'open',
  path: 'F:\\Semester 5\\Introductiob to AI\\Lab1\\HouseSales.txt'
}

Is there any way where I can write to a file in a very big loop in JavaScript ? I have tried fs but I am not getting a solution. I think fs cannot help when it comes to writing to a file 1000s of times or more.

You should consider a more traditional approach. Namely, open the file outside the loop, only write bytes to the file inside the loop, and close the file after the loop. Should work just fine. fsOpen, fsWrite, fsClose — Randy Casburn
– Randy Casburn, Commented Oct 1, 2020 at 20:47
Yes. Fs has multiple different ways of doing the same thing (in this case writing to a file), so you can choose the one which suits you best. This one fails because it's asynchronous. It writes to the file in background while your loop continues. However your loop is much faster than the file write so you end up re-opening the file before the last write has finished. Try writeFileSync. — Vilx-
– Vilx-, Commented Oct 1, 2020 at 20:59

audzzy · Accepted Answer · 2020-10-01 20:52:04Z

3

you should create a stream before the loop and write to it in he loop:

var out = fs.createWriteStream("HouseSales.txt", { flags : 'a' });

a flag is for appending, it will create the file if it doesnt exist. and use this to write:

out.write(`M Slope : ${M}  C Intercept : ${C} MSE : ${MSE}`, 'utf-8');

finally (after the loop) close the stream:

out.end();

answered Oct 1, 2020 at 20:52

audzzy

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1 Comment

birgersp Over a year ago

should there be a newline in the string?

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