section4.9.md

Section 4.9: Avoiding race conditions when creating or using an existing directory

Due to Node's asynchronous nature, creating or using a directory by first:

• checking for its existence with fs.stat(), then
• creating or using it depending of the results of the existence check,

can lead to a race condition if the folder is created between the time of the check and the time of the creation. The method below wraps fs.mkdir() and fs.mkdirSync() in error-catching wrappers that let the exception pass if its code is EEXIST (already exists). If the error is something else, like EPERM (pemission denied), throw or pass an error like the native functions do.

Asynchronous version with fs.mkdir()

let fs = require('fs');

function mkdir (dirPath, callback) {
  fs.mkdir(dirPath, (err) => {
    callback(err && err.code !== 'EEXIST' ? err : null);
  });
}

mkdir('./existing-dir', (err) => {
  if (err)
    return console.error(err.code);
  // Do something with `./existingDir` here
});

Synchronous version with fs.mkdirSync()

function mkdirSync (dirPath) {
  try {
    fs.mkdirSync(dirPath);
  } catch(e) {
    if ( e.code !== 'EEXIST' ) throw e;
  }
}

mkdirSync('./existing-dir');