Writing files with Node.js

Writing a file

The easiest way to write to files in Node.js is to use the fs.writeFile() API.

const  = ('node:fs');

const  = 'Some content!';

.('/Users/joe/test.txt', ,  => {
  if () {
    .();
  } else {
    // file written successfully
  }
});

Writing a file synchronously

Alternatively, you can use the synchronous version fs.writeFileSync():

const  = ('node:fs');

const  = 'Some content!';

try {
  .('/Users/joe/test.txt', );
  // file written successfully
} catch () {
  .();
}

You can also use the promise-based fsPromises.writeFile() method offered by the fs/promises module:

const  = ('node:fs/promises');

async function () {
  try {
    const  = 'Some content!';
    await .('/Users/joe/test.txt', );
  } catch () {
    .();
  }
}

();

By default, this API will replace the contents of the file if it does already exist.

You can modify the default by specifying a flag:

fs.writeFile('/Users/joe/test.txt', content, { : 'a+' },  => {});

The flags you'll likely use are

Flag	Description	File gets created if it doesn't exist
`r+`	This flag opens the file for reading and writing	❌
`w+`	This flag opens the file for reading and writing and it also positions the stream at the beginning of the file	✅
`a`	This flag opens the file for writing and it also positions the stream at the end of the file	✅
`a+`	This flag opens the file for reading and writing and it also positions the stream at the end of the file	✅

You can find more information about the flags in the fs documentation.

Appending content to a file

Appending to files is handy when you don't want to overwrite a file with new content, but rather add to it.

Examples

A handy method to append content to the end of a file is fs.appendFile() (and its fs.appendFileSync() counterpart):

const  = ('node:fs');

const  = 'Some content!';

.('file.log', ,  => {
  if () {
    .();
  } else {
    // done!
  }
});

Example with Promises

Here is a fsPromises.appendFile() example:

const  = ('node:fs/promises');

async function () {
  try {
    const  = 'Some content!';
    await .('/Users/joe/test.txt', );
  } catch () {
    .();
  }
}

();

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