fetch-blob

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A Blob implementation in Node.js, originally from node-fetch.

Installation

npm install fetch-blob
Upgrading from 2x to 3x Updating from 2 to 3 should be a breeze since there is not many changes to the blob specification. The major cause of a major release is coding standards. - internal WeakMaps was replaced with private fields - internal Buffer.from was replaced with TextEncoder/Decoder - internal buffers was replaced with Uint8Arrays - CommonJS was replaced with ESM - The node stream returned by calling `blob.stream()` was replaced with whatwg streams - (Read "Differences from other blobs" for more info.)
Differences from other Blobs - Unlike NodeJS `buffer.Blob` (Added in: v15.7.0) and browser native Blob this polyfilled version can't be sent via PostMessage - This blob version is more arbitrary, it can be constructed with blob parts that isn't a instance of itself it has to look and behave as a blob to be accepted as a blob part. - The benefit of this is that you can create other types of blobs that don't contain any internal data that has to be read in other ways, such as the `BlobDataItem` created in `from.js` that wraps a file path into a blob-like item and read lazily (nodejs plans to [implement this][fs-blobs] as well) - The `blob.stream()` is the most noticeable differences. It returns a WHATWG stream now. to keep it as a node stream you would have to do: ```js import {Readable} from 'stream' const stream = Readable.from(blob.stream()) ```

Usage

// Ways to import
// (PS it's dependency free ESM package so regular http-import from CDN works too)
import Blob from 'fetch-blob'
import File from 'fetch-blob/file.js'

import {Blob} from 'fetch-blob'
import {File} from 'fetch-blob/file.js'

const {Blob} = await import('fetch-blob')


// Ways to read the blob:
const blob = new Blob(['hello, world'])

await blob.text()
await blob.arrayBuffer()
for await (let chunk of  blob.stream()) { ... }
blob.stream().getReader().read()
blob.stream().getReader({mode: 'byob'}).read(view)

Blob part backed up by filesystem

fetch-blob/from.js comes packed with tools to convert any filepath into either a Blob or a File It will not read the content into memory. It will only stat the file for last modified date and file size.

// The default export is sync and use fs.stat to retrieve size & last modified as a blob
import blobFromSync from 'fetch-blob/from.js'
import {File, Blob, blobFrom, blobFromSync, fileFrom, fileFromSync} from 'fetch-blob/from.js'

const fsFile = fileFromSync('./2-GiB-file.bin', 'application/octet-stream')
const fsBlob = await blobFrom('./2-GiB-file.mp4')

// Not a 4 GiB memory snapshot, just holds references
// points to where data is located on the disk
const blob = new Blob([fsFile, fsBlob, 'memory', new Uint8Array(10)])
console.log(blob.size) // ~4 GiB

blobFrom|blobFromSync|fileFrom|fileFromSync(path, [mimetype])

Creating Blobs backed up by other async sources

Our Blob & File class are more generic then any other polyfills in the way that it can accept any blob look-a-like item An example of this is that our blob implementation can be constructed with parts coming from BlobDataItem (aka a filepath) or from buffer.Blob, It dose not have to implement all the methods - just enough that it can be read/understood by our Blob implementation. The minium requirements is that it has Symbol.toStringTag, size, slice() and either a stream() or a arrayBuffer() method. If you then wrap it in our Blob or File new Blob([blobDataItem]) then you get all of the other methods that should be implemented in a blob or file

An example of this could be to create a file or blob like item coming from a remote HTTP request. Or from a DataBase

See the MDN documentation and tests for more details of how to use the Blob.