How to write file if parent folder doesn't exist?

Use mkdirp in combination with path.dirname first.

var mkdirp = require('mkdirp');
var fs = require('fs');
var getDirName = require('path').dirname;

function writeFile(path, contents, cb) {
  mkdirp(getDirName(path), function (err) {
    if (err) return cb(err);

    fs.writeFile(path, contents, cb);
  });
}

If the whole path already exists, mkdirp is a noop. Otherwise it creates all missing directories for you.

This module does what you want: https://npmjs.org/package/writefile . Got it when googling for "writefile mkdirp". This module returns a promise instead of taking a callback, so be sure to read some introduction to promises first. It might actually complicate things for you.

The function I gave works in any case.

I find that the easiest way to do this is to use the outputFile() method from the fs-extra module.

Almost the same as writeFile (i.e. it overwrites), except that if the parent directory does not exist, it's created. options are what you'd pass to fs.writeFile().

Example:

var fs = require('fs-extra');
var file = '/tmp/this/path/does/not/exist/file.txt'

fs.outputFile(file, 'hello!', function (err) {
    console.log(err); // => null

    fs.readFile(file, 'utf8', function (err, data) {
        console.log(data); // => hello!
    });
});

It also has promise support out of the box these days!.

Edit

NodeJS version 10.12.0 has added a native support for both mkdir and mkdirSync to create the parent director recursively with recursive: true option as the following:

fs.mkdirSync(targetDir, { recursive: true });

And if you prefer fs Promises API, you can write

fs.promises.mkdir(targetDir, { recursive: true });

Original Answer

Create the parent directories recursively if they do not exist! (Zero dependencies)

const fs = require('fs');
const path = require('path');

function mkDirByPathSync(targetDir, { isRelativeToScript = false } = {}) {
  const sep = path.sep;
  const initDir = path.isAbsolute(targetDir) ? sep : '';
  const baseDir = isRelativeToScript ? __dirname : '.';

  return targetDir.split(sep).reduce((parentDir, childDir) => {
    const curDir = path.resolve(baseDir, parentDir, childDir);
    try {
      fs.mkdirSync(curDir);
    } catch (err) {
      if (err.code === 'EEXIST') { // curDir already exists!
        return curDir;
      }

      // To avoid `EISDIR` error on Mac and `EACCES`-->`ENOENT` and `EPERM` on Windows.
      if (err.code === 'ENOENT') { // Throw the original parentDir error on curDir `ENOENT` failure.
        throw new Error(`EACCES: permission denied, mkdir '${parentDir}'`);
      }

      const caughtErr = ['EACCES', 'EPERM', 'EISDIR'].indexOf(err.code) > -1;
      if (!caughtErr || caughtErr && curDir === path.resolve(targetDir)) {
        throw err; // Throw if it's just the last created dir.
      }
    }

    return curDir;
  }, initDir);
}

Usage

// Default, make directories relative to current working directory.
mkDirByPathSync('path/to/dir');

// Make directories relative to the current script.
mkDirByPathSync('path/to/dir', {isRelativeToScript: true});

// Make directories with an absolute path.
mkDirByPathSync('/path/to/dir');

Demo

Try It!

Explanations

• [UPDATE] This solution handles platform-specific errors like EISDIR for Mac and EPERM and EACCES for Windows.
• This solution handles both relative and absolute paths.
• In the case of relative paths, target directories will be created (resolved) in the current working directory. To Resolve them relative to the current script dir, pass {isRelativeToScript: true}.
• Using path.sep and path.resolve(), not just / concatenation, to avoid cross-platform issues.
• Using fs.mkdirSync and handling the error with try/catch if thrown to handle race conditions: another process may add the file between the calls to fs.existsSync() and fs.mkdirSync() and causes an exception.
  • The other way to achieve that could be checking if a file exists then creating it, I.e, if (!fs.existsSync(curDir) fs.mkdirSync(curDir);. But this is an anti-pattern that leaves the code vulnerable to race conditions.
• Requires Node v6 and newer to support destructuring. (If you have problems implementing this solution with old Node versions, just leave me a comment)