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A Blob implementation in Node.js, originally fromnode-fetch.

Use the built-inBlob in Node.js 18 and later.

npm install fetch-blob

import{Readable}from'stream'conststream=Readable.from(blob.stream())

// Ways to importimport{Blob}from'fetch-blob'import{File}from'fetch-blob/file.js'const{ Blob}=awaitimport('fetch-blob')// Ways to read the blob:constblob=newBlob(['hello, world'])awaitblob.text()awaitblob.arrayBuffer()forawait(letchunkofblob.stream()){ ...}blob.stream().getReader().read()blob.stream().getReader({mode:'byob'}).read(view)

fetch-blob/from.js comes packed with tools to convert any filepath into either a Blob or a FileIt 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 blobimport{File,Blob,blobFrom,blobFromSync,fileFrom,fileFromSync}from'fetch-blob/from.js'constfsFile=fileFromSync('./2-GiB-file.bin','application/octet-stream')constfsBlob=awaitblobFrom('./2-GiB-file.mp4')// Not a 4 GiB memory snapshot, just holds references// points to where data is located on the diskconstblob=newBlob([fsFile,fsBlob,'memory',newUint8Array(10)])console.log(blob.size)// ~4 GiB

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

(requiresFinalizationRegistry - node v14.6)

When using bothcreateTemporaryBlob andcreateTemporaryFilethen you will write data to the temporary folder in their respective OS.The arguments can be anything thatfsPromises.writeFile supports. NodeJSv14.17.0+ also supports writing (async)Iterable streams and passing in aAbortSignal, so both NodeJS stream and whatwg streams are supported. When thefile have been written it will return a Blob/File handle with a references tothis temporary location on the disk. When you no longer have a references tothis Blob/File anymore and it have been GC then it will automatically be deleted.

This files are also unlinked upon exiting the process.

import{createTemporaryBlob,createTemporaryFile}from'fetch-blob/from.js'constreq=newRequest('https://httpbin.org/image/png')constres=awaitfetch(req)consttype=res.headers.get('content-type')constsignal=req.signalletblob=awaitcreateTemporaryBlob(res.body,{ type, signal})// const file = createTemporaryBlob(res.body, 'img.png', { type, signal })blob=undefined// loosing references will delete the file from disk

• createTemporaryBlob(data, { type, signal })
• createTemporaryFile(data, FileName, { type, signal, lastModified })

Our Blob & File class are more generic then any other polyfills in the way that it can accept any blob look-a-like itemAn example of this is that our blob implementation can be constructed with parts coming fromBlobDataItem (aka a filepath) or frombuffer.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 hasSymbol.toStringTag,size,slice(),stream() methods (the stream methodcan be as simple as being a sync or async iterator that yields Uint8Arrays. If you then wrap it in our Blob or Filenew Blob([blobDataItem]) then you get all of the other methods that should be implemented in a blob or file (aka: text(), arrayBuffer() and type and a ReadableStream)

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 theMDN documentation andtests for more details of how to use the Blob.