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FileSystem module reference

The fs/promises module provides utilities for working with files and can be accessed using an import:

import { readFile } from 'fs/promises';

const content = await readFile('./foo.txt', 'utf8');

Path resolution​

All fs/promises paths are resolved relative to the directory of the running operation or script (equivalent to using path.resolve from that directory).

Project sandbox​

Kreya scripts can only access files within the Kreya project directory and its subdirectories; access outside this sandbox is blocked.

Functions​

appendFile()​

Call Signature​

function appendFile(
   path: string, 
   data: string, 
encodingName?: string): Promise<void>;

Appends data to a file, replacing the file if it already exists.

Parameters​
ParameterTypeDescription
pathstringThe path to the file (resolved relative to the directory of the running script/operation).
datastringThe data to append.
encodingName?stringThe encoding to use: utf8 (default), utf16le, ascii, hex, base64, or base64url.
Returns​

Promise<void>

Call Signature​

function appendFile(
   path: string, 
   data: string, 
options: FileAppendOptions): Promise<void>;

Appends data to a file.

Parameters​
ParameterTypeDescription
pathstringThe path to the file (resolved relative to the directory of the running script/operation).
datastringThe data to append.
optionsFileAppendOptionsThe options.
Returns​

Promise<void>

Call Signature​

function appendFile(path: string, data: Uint8Array): Promise<void>;

Appends data to a file, replacing the file if it already exists.

Parameters​
ParameterTypeDescription
pathstringThe path to the file (resolved relative to the directory of the running script/operation).
dataUint8ArrayThe data to append.
Returns​

Promise<void>

Call Signature​

function appendFile(
   path: string, 
   data: Uint8Array, 
options: FileAppendOptions): Promise<void>;

Appends data to a file, replacing the file if it already exists (depending on options.flag).

Parameters​
ParameterTypeDescription
pathstringThe path to the file (resolved relative to the directory of the running script/operation).
dataUint8ArrayThe data to append.
optionsFileAppendOptionsThe options.
Returns​

Promise<void>

Call Signature​

function appendFile(
   path: string, 
   data: Uint8Array, 
options: FileAppendOptions): Promise<void>;

Appends data to a file, replacing the file if it already exists (depending on options.flag).

Parameters​
ParameterTypeDescription
pathstringThe path to the file (resolved relative to the directory of the running script/operation).
dataUint8ArrayThe data to append.
optionsFileAppendOptionsThe options.
Returns​

Promise<void>

readFile()​

Call Signature​

function readFile(path: string): Promise<Uint8Array<ArrayBufferLike>>;

Reads the entire content of a file.

Parameters​
ParameterTypeDescription
pathstringThe path to the file (resolved relative to the directory of the running script/operation).
Returns​

Promise<Uint8Array<ArrayBufferLike>>

The data of the file.

Call Signature​

function readFile(path: string, encodingName: string): Promise<string>;

Reads the entire content of a file.

Parameters​
ParameterTypeDescription
pathstringThe path to the file (resolved relative to the directory of the running script/operation).
encodingNamestringThe encoding to use: utf8 (default), utf16le, ascii, hex, base64, or base64url.
Returns​

Promise<string>

The contents of the file.

Call Signature​

function readFile(path: string, options: FileReadOptions): Promise<Uint8Array<ArrayBufferLike>> | Promise<string>;

Reads the entire content of a file.

Parameters​
ParameterTypeDescription
pathstringThe path of the file (resolved relative to the running script).
optionsFileReadOptionsThe options to read the file, including encoding.
Returns​

Promise<Uint8Array<ArrayBufferLike>> | Promise<string>

The file content as string if an encoding is provided, as Uint8Array otherwise.

writeFile()​

Call Signature​

function writeFile(
   path: string, 
   data: string, 
encodingName?: string): Promise<void>;

Writes data to a file, replacing the file if it already exists.

Parameters​
ParameterTypeDescription
pathstringThe path to the file (resolved relative to the directory of the running script/operation).
datastringThe data to write.
encodingName?stringThe encoding to use: utf8 (default), utf16le, ascii, hex, base64, or base64url.
Returns​

Promise<void>

Call Signature​

function writeFile(
   path: string, 
   data: string, 
options: FileWriteOptions): Promise<void>;

Writes data to a file, replacing the file if it already exists (depending on options.flag).

Parameters​
ParameterTypeDescription
pathstringThe path to the file (resolved relative to the directory of the running script/operation).
datastringThe data to write.
optionsFileWriteOptionsThe options.
Returns​

Promise<void>

Call Signature​

function writeFile(path: string, data: Uint8Array): Promise<void>;

Writes data to a file, replacing the file if it already exists.

Parameters​
ParameterTypeDescription
pathstringThe path to the file (resolved relative to the directory of the running script/operation).
dataUint8ArrayThe data to write.
Returns​

Promise<void>

Call Signature​

function writeFile(
   path: string, 
   data: Uint8Array, 
options: FileWriteOptions): Promise<void>;

Writes data to a file, replacing the file if it already exists (depending on options.flag).

Parameters​
ParameterTypeDescription
pathstringThe path to the file (resolved relative to the directory of the running script/operation).
dataUint8ArrayThe data to write.
optionsFileWriteOptionsThe options.
Returns​

Promise<void>

Call Signature​

function writeFile(
   path: string, 
   data: Uint8Array, 
options: FileWriteOptions): Promise<void>;

Writes data to a file, replacing the file if it already exists (depending on options.flag).

Parameters​
ParameterTypeDescription
pathstringThe path to the file (resolved relative to the directory of the running script/operation).
dataUint8ArrayThe data to write.
optionsFileWriteOptionsThe options.
Returns​

Promise<void>

Type Aliases​

FileAppendOptions​

type FileAppendOptions = {
  encoding?: string;
  flag?: string;
};

Options to append to files.

Properties​

encoding?​
optional encoding?: string;

The encoding to use: utf8 (default), utf16le, ascii, hex, base64, or base64url.

flag?​
optional flag?: string;

File system flag (default a). Supported values: a, ax, a+, ax+, as, as+, w, wx, w+, wx+, r, rs, r+, rs+. Use an x suffix to fail if the file exists, + to allow reading, and s to open synchronously. See also https://nodejs.org/api/fs.html#file-system-flags.

FileReadOptions​

type FileReadOptions = {
  encoding?: string;
};

Options when reading a file.

Properties​

encoding?​
optional encoding?: string;

The encoding to use: utf8 (default), utf16le, ascii, hex, base64, or base64url.

FileWriteOptions​

type FileWriteOptions = {
  encoding?: string;
  flag?: string;
};

Options to write files.

Properties​

encoding?​
optional encoding?: string;

The encoding to use: utf8 (default), utf16le, ascii, hex, base64, or base64url.

flag?​
optional flag?: string;

File system flag (default w). Supported values: w, wx, w+, wx+, a, ax, a+, ax+, as, as+, r, rs, r+, rs+. Use an x suffix to fail if the file exists, + to allow reading, and s to open synchronously. See also https://nodejs.org/api/fs.html#file-system-flags.