How to not overwrite file in node.js

问题:

I want to make this code to change filename if file exists instead of overwritng it.

var fileName = 'file';

fs.writeFile(fileName + '.txt', 'Random text', function (err) {
  if (err) throw err;
  console.log('It\'s saved!');
});

Something like:

var fileName = 'file',
    checkFileName = fileName,
    i = 0;

while(fileExists(checkFileName + '.txt')) {
  i++;
  checkFileName = fileName + '-' + i;
} // file-1, file-2, file-3...

fileName = checkFileName;

fs.writeFile(fileName + '.txt', 'Random text', function (err) {
  if (err) throw err;
  console.log('It\'s saved!');
});

How can I make "fileExists" function, considering that fs.exists() is now deprecated and fs.statSync() or fs.accessSync() throws error if file doesn't exist. Maybe there is a better way to achieve this?

回答1:

use writeFile with the third argument set to {flag: "wx"} (see fs.open for an overview of flags). That way, it fails when the file already exists and it also avoids the possible race condition that the file is created between the exists and writeFile call.

Example code to write file under a different name when it already exist.

fs = require('fs');


var filename = "test";

function writeFile() {
  fs.writeFile(filename, "some data", { flag: "wx" }, function(err) {
    if (err) {
      console.log("file " + filename + " already exists, testing next");
      filename = filename + "0";
      writeFile();
    }
    else {
      console.log("Succesfully written " + filename);
    }
  });

}
writeFile();