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 module "node:fs"fs = var require: NodeJS.Require
(id: string) => anyrequire('node:fs');

const const content: "Some content!"content = 'Some content!';

module "node:fs"fs.function writeFile(path: fs.PathOrFileDescriptor, data: string | NodeJS.ArrayBufferView, callback: fs.NoParamCallback): void (+1 overload)writeFile('/Users/joe/test.txt', const content: "Some content!"content, err: NodeJS.ErrnoException | nullerr => {
  if (err: NodeJS.ErrnoException | nullerr) {
    var console: Consoleconsole.Console.error(message?: any, ...optionalParams: any[]): void (+1 overload)error(err: NodeJS.ErrnoExceptionerr);
  } else {
    // file written successfully
  }
});

Writing a file synchronously

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

const module "node:fs"fs = var require: NodeJS.Require
(id: string) => anyrequire('node:fs');

const const content: "Some content!"content = 'Some content!';

try {
  module "node:fs"fs.function writeFileSync(file: fs.PathOrFileDescriptor, data: string | NodeJS.ArrayBufferView, options?: fs.WriteFileOptions): voidwriteFileSync('/Users/joe/test.txt', const content: "Some content!"content);
  // file written successfully
} catch (var err: unknownerr) {
  var console: Consoleconsole.Console.error(message?: any, ...optionalParams: any[]): void (+1 overload)error(var err: unknownerr);
}

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

const module "node:fs/promises"fs = var require: NodeJS.Require
(id: string) => anyrequire('node:fs/promises');

async function function example(): Promise<void>example() {
  try {
    const const content: "Some content!"content = 'Some content!';
    await module "node:fs/promises"fs.function writeFile(file: PathLike | fs.FileHandle, data: string | NodeJS.ArrayBufferView | Iterable<string | NodeJS.ArrayBufferView> | AsyncIterable<string | NodeJS.ArrayBufferView> | Stream, options?: (ObjectEncodingOptions & {
    mode?: Mode | undefined;
    flag?: OpenMode | undefined;
    flush?: boolean | undefined;
} & EventEmitter<T extends EventMap<...> = DefaultEventMap>.Abortable) | BufferEncoding | null): Promise<void>writeFile('/Users/joe/test.txt', const content: "Some content!"content);
  } catch (function (local var) err: unknownerr) {
    var console: Consoleconsole.Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)log(function (local var) err: unknownerr);
  }
}

function example(): Promise<void>example();

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, { flag: stringflag: 'a+' }, err: anyerr => {});

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 module "node:fs"fs = var require: NodeJS.Require
(id: string) => anyrequire('node:fs');

const const content: "Some content!"content = 'Some content!';

module "node:fs"fs.function appendFile(file: fs.PathOrFileDescriptor, data: string | Uint8Array, callback: fs.NoParamCallback): void (+1 overload)appendFile('file.log', const content: "Some content!"content, err: NodeJS.ErrnoException | nullerr => {
  if (err: NodeJS.ErrnoException | nullerr) {
    var console: Consoleconsole.Console.error(message?: any, ...optionalParams: any[]): void (+1 overload)error(err: NodeJS.ErrnoExceptionerr);
  } else {
    // done!
  }
});

Example with Promises

Here is a fsPromises.appendFile() example:

const module "node:fs/promises"fs = var require: NodeJS.Require
(id: string) => anyrequire('node:fs/promises');

async function function example(): Promise<void>example() {
  try {
    const const content: "Some content!"content = 'Some content!';
    await module "node:fs/promises"fs.function appendFile(path: PathLike | fs.FileHandle, data: string | Uint8Array, options?: (ObjectEncodingOptions & fs.FlagAndOpenMode & {
    flush?: boolean | undefined;
}) | BufferEncoding | null): Promise<void>appendFile('/Users/joe/test.txt', const content: "Some content!"content);
  } catch (function (local var) err: unknownerr) {
    var console: Consoleconsole.Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)log(function (local var) err: unknownerr);
  }
}

function example(): Promise<void>example();

Reading files with Node.js Working with folders in Node.js