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write

Bun

Symbol

write

function write(destination: BunFile | S3File | PathLike, input: string | ArrayBufferLike | Blob | TypedArray<ArrayBufferLike> | BlobPart[], options?: { createPath: boolean; mode: number }): Promise<number>

Use the fastest syscalls available to copy from input into destination.

If destination exists, it must be a regular file or symlink to a file. If destination's directory does not exist, it will be created by default.

@param destination

The file or file path to write to

@param input

The data to copy into destination.

@returns

A promise that resolves with the number of bytes written.

function write(destination: BunFile, input: Response, options?: { createPath: boolean }): Promise<number>

Persist a Response body to disk.

@param destination

The file to write to. If the file doesn't exist, it will be created and if the file does exist, it will be overwritten. If input's size is less than destination's size, destination will be truncated.

@param input

Response object

@returns

A promise that resolves with the number of bytes written.

function write(destinationPath: PathLike, input: Response, options?: { createPath: boolean }): Promise<number>

Persist a Response body to disk.

@param destinationPath

The file path to write to. If the file doesn't exist, it will be created and if the file does exist, it will be overwritten. If input's size is less than destination's size, destination will be truncated.

@param input

Response object

@returns

A promise that resolves with the number of bytes written.

function write(destination: BunFile, input: BunFile, options?: { createPath: boolean }): Promise<number>

Use the fastest syscalls available to copy from input into destination.

If destination exists, it must be a regular file or symlink to a file.

On Linux, this uses copy_file_range.

On macOS, when the destination doesn't already exist, this uses clonefile() and falls back to fcopyfile()

@param destination

The file to write to. If the file doesn't exist, it will be created and if the file does exist, it will be overwritten. If input's size is less than destination's size, destination will be truncated.

@param input

The file to copy from.

@returns

A promise that resolves with the number of bytes written.

function write(destinationPath: PathLike, input: BunFile, options?: { createPath: boolean }): Promise<number>

Use the fastest syscalls available to copy from input into destination.

If destination exists, it must be a regular file or symlink to a file.

On Linux, this uses copy_file_range.

On macOS, when the destination doesn't already exist, this uses clonefile() and falls back to fcopyfile()

@param destinationPath

The file path to write to. If the file doesn't exist, it will be created and if the file does exist, it will be overwritten. If input's size is less than destination's size, destination will be truncated.

@param input

The file to copy from.

@returns

A promise that resolves with the number of bytes written.

Referenced types

interface BunFile

Blob powered by the fastest system calls available for operating on files.

This Blob is lazy. That means it won't do any work until you read from it.

  • size will not be valid until the contents of the file are read at least once.
  • type is auto-set based on the file extension when possible
const file = Bun.file("./hello.json");
console.log(file.type); // "application/json"
console.log(await file.text()); // '{"hello":"world"}'
  • lastModified: number

    A UNIX timestamp indicating when the file was last modified.

  • readonly name?: string

    The name or path of the file, as specified in the constructor.

  • readonly size: number
  • readonly type: string

  • Returns a promise that resolves to the contents of the blob as an ArrayBuffer

  • bytes(): Promise<Uint8Array<ArrayBufferLike>>

    Returns a promise that resolves to the contents of the blob as a Uint8Array (array of bytes) its the same as new Uint8Array(await blob.arrayBuffer())

  • delete(): Promise<void>

    Deletes the file (same as unlink)

  • exists(): Promise<boolean>

    Does the file exist?

    This returns true for regular files and FIFOs. It returns false for directories. Note that a race condition can occur where the file is deleted or renamed after this is called but before you open it.

    This does a system call to check if the file exists, which can be slow.

    If using this in an HTTP server, it's faster to instead use return new Response(Bun.file(path)) and then an error handler to handle exceptions.

    Instead of checking for a file's existence and then performing the operation, it is faster to just perform the operation and handle the error.

    For empty Blob, this always returns true.

  • formData(): Promise<FormData>

    Read the data from the blob as a FormData object.

    This first decodes the data from UTF-8, then parses it as a multipart/form-data body or a application/x-www-form-urlencoded body.

    The type property of the blob is used to determine the format of the body.

    This is a non-standard addition to the Blob API, to make it conform more closely to the BodyMixin API.

  • json(): Promise<any>

    Read the data from the blob as a JSON object.

    This first decodes the data from UTF-8, then parses it as JSON.

  • slice(begin?: number, end?: number, contentType?: string): BunFile

    Offset any operation on the file starting at begin and ending at end. end is relative to 0

    Similar to TypedArray.subarray. Does not copy the file, open the file, or modify the file.

    If begin > 0, () will be slower on macOS

    @param begin

    start offset in bytes

    @param end

    absolute offset in bytes (relative to 0)

    @param contentType

    MIME type for the new BunFile

    slice(begin?: number, contentType?: string): BunFile

    Offset any operation on the file starting at begin

    Similar to TypedArray.subarray. Does not copy the file, open the file, or modify the file.

    If begin > 0, Bun.write() will be slower on macOS

    @param begin

    start offset in bytes

    @param contentType

    MIME type for the new BunFile

    slice(contentType?: string): BunFile

    Slice the file from the beginning to the end, optionally with a new MIME type.

    @param contentType

    MIME type for the new BunFile

  • stat(): Promise<Stats>

    Provides useful information about the file.

  • stream(): ReadableStream<Uint8Array<ArrayBufferLike>>

    Returns a readable stream of the blob's contents

  • text(): Promise<string>

    Returns a promise that resolves to the contents of the blob as a string

  • write(data: string | ArrayBuffer | SharedArrayBuffer | Request | Response | BunFile | ArrayBufferView<ArrayBufferLike>, options?: { highWaterMark: number }): Promise<number>

    Write data to the file. This is equivalent to using Bun.write with a BunFile.

    @param data

    The data to write.

    @param options

    The options to use for the write.

  • writer(options?: { highWaterMark: number }): FileSink

    Incremental writer for files and pipes.

interface S3File

Represents a file in an S3-compatible storage service. Extends the Blob interface for compatibility with web APIs.

  • readonly bucket?: string

    The bucket name containing the file.

    const file = s3.file("s3://my-bucket/file.txt");
   console.log(file.bucket); // "my-bucket"
  • readonly name?: string

    The name or path of the file in the bucket.

    const file = s3.file("folder/image.jpg");
console.log(file.name); // "folder/image.jpg"
  • readonly readable: ReadableStream

    Gets a readable stream of the file's content. Useful for processing large files without loading them entirely into memory.

    // Basic streaming read
    const stream = file.stream();
    for await (const chunk of stream) {
      console.log('Received chunk:', chunk);
    }
  • readonly size: number
  • readonly type: string

  • Returns a promise that resolves to the contents of the blob as an ArrayBuffer

  • bytes(): Promise<Uint8Array<ArrayBufferLike>>

    Returns a promise that resolves to the contents of the blob as a Uint8Array (array of bytes) its the same as new Uint8Array(await blob.arrayBuffer())

  • delete(): Promise<void>

    Deletes the file from S3.

    @returns

    Promise that resolves when deletion is complete

    // Basic deletion
    await file.delete();
  • exists(): Promise<boolean>

    Checks if the file exists in S3. Uses HTTP HEAD request to efficiently check existence without downloading.

    @returns

    Promise resolving to true if file exists, false otherwise

    // Basic existence check
   if (await file.exists()) {
     console.log("File exists in S3");
   }
  • formData(): Promise<FormData>

    Read the data from the blob as a FormData object.

    This first decodes the data from UTF-8, then parses it as a multipart/form-data body or a application/x-www-form-urlencoded body.

    The type property of the blob is used to determine the format of the body.

    This is a non-standard addition to the Blob API, to make it conform more closely to the BodyMixin API.

  • json(): Promise<any>

    Read the data from the blob as a JSON object.

    This first decodes the data from UTF-8, then parses it as JSON.

  • presign(options?: S3FilePresignOptions): string

    Generates a presigned URL for the file. Allows temporary access to the file without exposing credentials.

    @param options

    Configuration for the presigned URL

    @returns

    Presigned URL string

    // Basic download URL
    const url = file.presign({
      expiresIn: 3600 // 1 hour
    });
  • slice(begin?: number, end?: number, contentType?: string): S3File

    Creates a new S3File representing a slice of the original file. Uses HTTP Range headers for efficient partial downloads.

    @param begin

    Starting byte offset

    @param end

    Ending byte offset (exclusive)

    @param contentType

    Optional MIME type for the slice

    @returns

    A new S3File representing the specified range

    // Reading file header
    const header = file.slice(0, 1024);
    const headerText = await header.text();
    slice(begin?: number, contentType?: string): S3File
    slice(contentType?: string): S3File
  • stat(): Promise<S3Stats>

    Get the stat of a file in an S3-compatible storage service.

    @returns

    Promise resolving to S3Stat

  • text(): Promise<string>

    Returns a promise that resolves to the contents of the blob as a string

  • write(data: string | ArrayBuffer | SharedArrayBuffer | Request | Response | Blob | BunFile | ArrayBufferView<ArrayBufferLike> | S3File, options?: S3Options): Promise<number>

    Uploads data to S3. Supports various input types and automatically handles large files.

    @param data

    The data to upload

    @param options

    Upload configuration options

    @returns

    Promise resolving to number of bytes written

    // Writing string data
    await file.write("Hello World", {
      type: "text/plain"
    });

  • Creates a writable stream for uploading data. Suitable for large files as it uses multipart upload.

    @param options

    Configuration for the upload

    @returns

    A NetworkSink for writing data

    // Basic streaming write
    const writer = file.writer({
      type: "application/json"
    });
    writer.write('{"hello": ');
    writer.write('"world"}');
    await writer.end();
type PathLike = string | NodeJS.TypedArray | ArrayBufferLike | URL

class Blob

A file-like object of immutable, raw data. Blobs represent data that isn't necessarily in a JavaScript-native format. The File interface is based on Blob, inheriting blob functionality and expanding it to support files on the user's system.

MDN Reference

  • readonly size: number
  • readonly type: string

  • Returns a promise that resolves to the contents of the blob as an ArrayBuffer

  • bytes(): Promise<Uint8Array<ArrayBufferLike>>

    Returns a promise that resolves to the contents of the blob as a Uint8Array (array of bytes) its the same as new Uint8Array(await blob.arrayBuffer())

  • formData(): Promise<FormData>

    Read the data from the blob as a FormData object.

    This first decodes the data from UTF-8, then parses it as a multipart/form-data body or a application/x-www-form-urlencoded body.

    The type property of the blob is used to determine the format of the body.

    This is a non-standard addition to the Blob API, to make it conform more closely to the BodyMixin API.

  • json(): Promise<any>

    Read the data from the blob as a JSON object.

    This first decodes the data from UTF-8, then parses it as JSON.

  • slice(start?: number, end?: number, contentType?: string): Blob
  • stream(): ReadableStream<Uint8Array<ArrayBufferLike>>

    Returns a readable stream of the blob's contents

  • text(): Promise<string>

    Returns a promise that resolves to the contents of the blob as a string

type BlobPart = string | Blob | BufferSource

class Response

This Fetch API interface represents the response to a request.

MDN Reference