know if there is a file so as not to write it

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know if there is a file so as not to write it

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#1 by (2 votes)

1

Should I use this function?

fs.exists (path, callback)

I do not know how to do the function to know if the file with the same name already exists, and if not then create it

my function is:

function escribir(archivo,data){
fs.stat('./archivos/'+archivo+'.txt', function(err, stat) {
if(err == null) {
    console.log('File exists');
} else if(err.code == 'ENOENT') {

    fs.writeFile('./archivos/'+archivo+'.txt', data, function(err) {
    if( err ){
        console.log( err );
    }
    else{
        console.log('Se ha escrito correctamente');
    }
    });
} else {
    console.log('Some other error: ', err.code);
}

}); }

javascript nodejs

asked by hubman 05.10.2016 в 03:54

source

1 answer

Haskell, division without div Exceptions order to validate java date

score 2 · Accepted Answer

You have some options, let's see some.

Synchronous

If you prefer the synchronous way, there are a couple of methods in the API that you can use.

fs # accessSync

This method checks if a file is accessible. If it is not, that is, if it does not exist, it will throw an exception.

try {
  if(fs.accessSync('/archivo.dat')) {
    // existe
  }
} catch (e) {
  // no existe
}

You can create a wrapper for this:

function fileExists(path) {
  try {
    if(fs.accessSync('/archivo.dat')) {
      return true;
    }
  } catch (e) {
    return false;
  }
}

fs # statSync

The previous solution is valid, but what would happen if there is a directory and a file with the same name? What would happen is that it would not throw any exception and if we forget this, it can cause us a headache when debugging.

The most viable solution would be statSync . This function lets you know if the file found is a directory or file.

function fileExists(path) {
  try {
    return fs.statSync(path).isFile();
  } catch (e) {
    return false;
  }
}

Keep in mind that there may be errors when trying to see the availability of a file / directory; in this case it would be better to return false only if the error code is ENOENT (error no entry): if(e.code === 'ENOENT') and relaunch the error or handle it if another error occurred, such as permisos .

If we wanted to adapt it to know if it is a directory, we will only have to change isFile by isDirectory .

Asynchronous

The asynchronous mode of the functions is very similar, the difference is that they receive a callback.

function fileExists(file, cb) {
  fs.stat(file, (err, stats) => {
    if (err) {
      if (err.code === 'ENOENT') {
        return cb(null, false);
      } else { // en caso de otro error
        return cb(err);
      }
    }
    // devolvemos el resultado de 'isFile'.
    return cb(null, stats.isFile());
  });
}

And it would be used in the following way:

fileExists('/archivo.dat', (err, exists) => {
  if(err) {
    // manejar otro tipo de error
  }
  if(exists) {
    // hacer algo si existe
  } else {
    // hacer algo si no existe
  }
});

Or if you prefer the promises, you can use the module es6-promise :

function existsFile(path) {
  return new Promise((resolve, reject) => {
    fs.stat(file, (err, stats) => {
        if (err) {
          if (err.code === 'ENOENT') {
           resolve(false);
          } else { // en caso de otro error
            reject(err);
          }
        }
        // devolvemos el resultado de 'isFile'.
        resolve(stats.isFile());
      });
  });
}

We would use it in the following way:

existsFile('/archivo.dat')
  .then(exists => {
    if(exists) {

    } else {

    }
  })
  .catch(err => {
    // manejar error
  });