Saving the file was as easy as creating a new Buffer with the Uint8Array object :
// chunk is the Uint8Array object
fs.appendFile(path, Buffer.from(chunk), function (err) {
if (err) {
fut.throw(err);
} else {
fut.return(chunk.length);
}
});
Top answer 1 of 3
38
Saving the file was as easy as creating a new Buffer with the Uint8Array object :
// chunk is the Uint8Array object
fs.appendFile(path, Buffer.from(chunk), function (err) {
if (err) {
fut.throw(err);
} else {
fut.return(chunk.length);
}
});
2 of 3
37
Building on Karl.S answer, this worked for me, outside of any framework:
fs.appendFileSync(outfile, Buffer.from(arrayBuffer));
Chrisfrew
chrisfrew.in › blog › saving-images-in-node-js-using-fetch-with-array-buffer-and-buffer
Saving Images In Node.js: Using Fetch with arrayBuffer() and ...
June 4, 2020 - I also used the nice file-type package to attempt to determine the file type of the image, since the API doesn't tell you 🤷♂️ [^1]. ... import fs from "fs"; import fetch from "node-fetch"; import FileType from "file-type"; const API_URL_HERE = "your-api-url.whatever"; async function savePhotoFromAPI() { const response = await fetch(API_URL_HERE); const arrayBuffer = await response.arrayBuffer(); const buffer = Buffer.from(arrayBuffer); const fileType = await FileType.fromBuffer(buffer); if (fileType.ext) { const outputFileName = `yourfilenamehere.${fileType.ext}` fs.createWriteStream(outputFileName).write(buffer); } else { console.log('File type could not be reliably determined!
Create image from ArrayBuffer in Nodejs - javascript
I'm trying to create an image file from chunks of ArrayBuffers. More on stackoverflow.com
node.js - Write ArrayBuffer to file in NodeJs - Stack Overflow
I am using Microsoft Cognitive Service Speech SDK for Nodejs to convert text to speech. The SDK is giving me the resulting audio as ArrayBuffer. How do I write this ArrayBuffer to an mp3 file or u... More on stackoverflow.com
ELI5: File, Uint8Array, Buffer, Arraybuffer, BytesArray, Blob…
A digital system, like a computer works on digital data, thus things which can be represented as digits. Or simpler: Computer sees a bit of numbers and works on them. Also a text is just a long number. Some time ago, one decided to have computers work on binary digits and to group 8 out of those as the typical size. That is a byte. (There were computers using other byte sizes, that's why sometimes, especially in network protocols, it is called octet) With a byte of eight bits you can represent 256 values. (From 0 to 255) over multiple decades there were discussions on representing text (actually that was prr-computer already with telegraphs etc) and one found the ASCII rules to map between numeric values and characters. Each letter in the English alphabet got a code. Thus the word Hello becomes the sequence of numbers 72 101 108 108 111 Now decimal system ia nice when counting with fingers, but not so good for a binary machine. As said we have the byte, thus instead ten digits is inconvenient so we use a number system with base 16, thus any digit can not only have ten different values (0 to 9) but 16 (0 to 9 and A to F) Thus the same numbers as above can be written in hex 0x48 0x65 0x6C 0x6C 0x6F Now each byte is represented by two hex digits which gives a nice structure (and if you notice that 0x41 is A and 0x61 is a you start to understand ASCII) Now over time 256 characters wasn't enough for represting text in all languages, so after many years and messing around with different code pages and encodings smart folks came up with Unicode and Utf-8 to encode all characters. Won't go there too deep, but in essence utf-8 uses the ASCII table for the first 128 characters (half a byte, the lower half) and all other characters use multiple bytes. The German letter Ä fornisntance is 0xC3 0x48. In addition the Unicode standard has specific rules on sorting and comparing those values and some fancy transformations. (Sorting rules are even language dependent, so the German Ä can be sorted like AE, behind Z or simply as A) Wenn Browsers and JavaScript were created it was decided that a string in JavaScirpt shall be Unicode data. This is logical as websites are full of human readable text and properties of Unicode are good (well, the story is more complicated there, but good enough) This was good for the time where Web was working with simple websites and JavaScript was doing minor text manipulation. However for lower layers of the compitong stack data is just a sequence of bytes. In memory you have bytes. A file is a sequence of bytes. The meaning of those bytes might be Unicode text, might be an image, might even be bianry program code all are just bytes. The difference is only in the one looking at it. Now treating all data as unicode string will do harm, as they have all the assumptions on top where only specific byte sequences are valid and so on. So something else had to be added. And in fact different groups added different things. Before we can explain that, one step more is needed: as said interpretation depends on who looks at the data. So back to our numbers and from decimal and hex to binary. As said 8 bit are a byte. The number 1 in binary with it 8 bits would look like 0b00000001 Here using 0b as prefix, so you interpret it as binary, not hey, not decimal. The value 127 inn inary looks like this: 0b01111111 all bits, but the first set. Now something fancy happens when we set the first bit to 1 as well: 0b11111111 This can either be 255 or -1. Wait what negative!? You will ask: Yes, there eisna problem with these numbers: Our byte has to represent negative numbers as well. And then the first digit tells us whether it's negative or positive. And whenever we look at the byte we have to make a choice how we look at it. Is it a text character? Is it a positive number? A negative number? The byte doesn't know and doesn't care only we when looking at it. Now the Uint8Array enters! By giving a sequence of bytes (some area in memory) to an Uint8Buffer we tell it "look at those bytes and treat tit like a sequence of bytes, where each byte is a 8 bit unsigned number" and by that we can work with those.bytes and each byte will be a number 0 to 256 and whatever we do with the array decides on what it does with those bytes. Maybe it is a pixel in an image, maybe an frequency on an audio file, maybe ... Now another term there eisnthe Buffer. A buffer is just some area in memory. An arrayBuffer is "this is my area of memory, but I haven't yet decided how i will interpret it" I said Buffer, I said complicazednhsorory ... That tis that Node.js developers Hand this issue before ArrayBuffer d Uint8Array was defined, so they created their own thing, which is similar to an Unit8Array (modern versions of Buffer are built on Uint8Array) but don't be confused, buffer is a generic term for some data stored somewhere, which is distinct from Buffer, which is a type in Node.js. Now there ris a bit more. 256 is a bit low formmany purposes. So you can group multiple bytes and make them digits in a larger number. Quite typical are efor 4 byte, which are 32 bit. Thus a Int32Array takes 4 bytes at once from the underlying data (the ArrayBuffer, the buffer, the memory region) and makes it a 32 bit signed number (- 2147483648 to 2147483647) the Uint32Array (0 to 4294967295) and if that isn't enought there are big(u)int64Array, which look at 8 byte at a time, which is also the number of byte/bit a modern CPU can store in it's register, transfer though bus and process the best, hence 64bit architecture. The key thing is: memory (RAM, disk or any other form) in modern computers is just a sequence of bytes and the way you look at it decides on the meaning. The computer doesn't know and you have to tell it. Uint8Array is the typically representation for low level work. ArrayBuffer is when you haven't decided, yet and all else are more special. More on reddit.com
6
12
December 16, 2021sails.js - How to convert file to buffer in node.js? - Stack Overflow
If you're just now coming to this ... here: nodejs.org/api/… 2018-08-13T20:24:58.867Z+00:00 ... @ChasenBettinger thanks for the heads up -- updated to show the proper usage of Buffer 2018-08-14T17:12:43.237Z+00:00 ... If anyone here is a frontend developer, confused with backend operations, and was looking for File Object -> ... More on stackoverflow.com
GitHub
github.com › nodejs › node › issues › 42228
Allow ArrayBuffer as argument to writeFile and friends · Issue #42228 · nodejs/node
March 6, 2022 - (The fact this isn't possible is something I forget pretty much everytime I go to write an ArrayBuffer). I propose allowing fs.promises.writeFile("./some-file", someArrayBuffer) to work when someArrayBuffer is an ArrayBuffer.
Author: nodejs
Bun
bun.com › modules › node:buffer › file › arraybuffer
File.arrayBuffer method | Node.js buffer module | Bun
June 18, 2026 - Represents a raw buffer of binary data, which is used to store data for the different typed arrays. ArrayBuffers cannot be read from or written to directly, but can be passed to a typed array or DataView Object to interpret the raw buffer as needed.
Node.js
nodejs.org › api › buffer.html
Buffer | Node.js v26.11.1 Documentation
The intent is for type to convey the MIME media type of the data, however no validation of the type format is performed. Creates a new Blob object containing a concatenation of the given sources. <ArrayBuffer>, <TypedArray>, <DataView>, and <Buffer> sources are copied into the 'Blob' and can therefore be safely modified after the 'Blob' is created.
Top answer 1 of 3
3
Have you tried first converting it into a node.js. Buffer? (this is the native node.js Buffer interface, whereas ArrayBuffer is the interface for the browser and not completely supported for node.js write operations).
Something along the line of this should help:
all= fs.createWriteStream("out."+imgtype);
for(i=0; i<end; i++){
var buffer = new Buffer( new Uint8Array(picarray[i]) );
all.write(buffer);
}
all.end();
2 of 3
3
after spending some time i got this, it worked for me perfectly.
as mentioned by @Nick you will have to convert buffer array you recieved from browser in to nodejs Buffer.
var readWriteFile = function (req) {
var fs = require('fs');
var data = new Buffer(req);
fs.writeFile('fileName.png', data, 'binary', function (err) {
if (err) {
console.log("There was an error writing the image")
}
else {
console.log("The sheel file was written")
}
});
});
};
Untitled Publication
rajit.hashnode.dev › mastering-arraybuffer-in-javascript-a-guide-to-file-handling-with-expressjs-and-nextjs
Handle Files with ArrayBuffer in JavaScript, Express & Next
November 30, 2025 - You’ll often use both — ArrayBuffer in browser contexts (e.g., file readers, fetch API) and Buffer in Node.js. ... ArrayBuffer is a low-level way to handle binary data in JavaScript. It’s often used with typed arrays like Uint8Array to read/write bytes.
Stack Overflow
stackoverflow.com › questions › 67689044 › write-arraybuffer-to-file-in-nodejs
node.js - Write ArrayBuffer to file in NodeJs - Stack Overflow
May 25, 2021 - I am using Microsoft Cognitive Service Speech SDK for Nodejs to convert text to speech. The SDK is giving me the resulting audio as ArrayBuffer. How do I write this ArrayBuffer to an mp3 file or u...
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Global_Objects › ArrayBuffer
ArrayBuffer - JavaScript - MDN Web Docs
You cannot directly manipulate the contents of an ArrayBuffer; instead, you create one of the typed array objects or a DataView object which represents the buffer in a specific format, and use that to read and write the contents of the buffer. The ArrayBuffer() constructor creates a new ArrayBuffer of the given length in bytes. You can also get an array buffer from existing data, for example, from a Base64 string or from a local file.
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › API › FileReader › readAsArrayBuffer
FileReader: readAsArrayBuffer() method - Web APIs | MDN
July 26, 2024 - The readAsArrayBuffer() method of the FileReader interface is used to start reading the contents of a specified Blob or File. When the read operation is finished, the readyState property becomes DONE, and the loadend event is triggered. At that time, the result property contains an ArrayBuffer ...
W3Schools
w3schools.com › nodejs › nodejs_buffer.asp
Node.js Buffer Module
const fs = require('fs'); // Write buffer to file const writeBuffer = Buffer.from('Hello, Node.js!'); fs.writeFile('buffer.txt', writeBuffer, (err) => { if (err) throw err; console.log('File written successfully'); // Read file into buffer ...
Reddit
reddit.com › r/node › eli5: file, uint8array, buffer, arraybuffer, bytesarray, blob…
r/node on Reddit: ELI5: File, Uint8Array, Buffer, Arraybuffer, BytesArray, Blob…
December 16, 2021 -
I’m always ending up guessing.. I need to somehow understand. I have no idea what I’m doing when working with files. Just trying stuff until it works. Someone plz ELI5..
My current issue is getting a png file from Firebase storage which gives a “file” which I’m trying to add on a pdf, where the library expects a Uint8Array or Arraybuffer. I’ve been doing similar things before. But end up just guessing my way until it works, and this time.. well it doesn’t work. I guessed it all with no success. I don’t know what I’m doing so I guess I need to actually learn ;)
Top answer 1 of 2
36
A digital system, like a computer works on digital data, thus things which can be represented as digits. Or simpler: Computer sees a bit of numbers and works on them. Also a text is just a long number. Some time ago, one decided to have computers work on binary digits and to group 8 out of those as the typical size. That is a byte. (There were computers using other byte sizes, that's why sometimes, especially in network protocols, it is called octet) With a byte of eight bits you can represent 256 values. (From 0 to 255) over multiple decades there were discussions on representing text (actually that was prr-computer already with telegraphs etc) and one found the ASCII rules to map between numeric values and characters. Each letter in the English alphabet got a code. Thus the word Hello becomes the sequence of numbers 72 101 108 108 111 Now decimal system ia nice when counting with fingers, but not so good for a binary machine. As said we have the byte, thus instead ten digits is inconvenient so we use a number system with base 16, thus any digit can not only have ten different values (0 to 9) but 16 (0 to 9 and A to F) Thus the same numbers as above can be written in hex 0x48 0x65 0x6C 0x6C 0x6F Now each byte is represented by two hex digits which gives a nice structure (and if you notice that 0x41 is A and 0x61 is a you start to understand ASCII) Now over time 256 characters wasn't enough for represting text in all languages, so after many years and messing around with different code pages and encodings smart folks came up with Unicode and Utf-8 to encode all characters. Won't go there too deep, but in essence utf-8 uses the ASCII table for the first 128 characters (half a byte, the lower half) and all other characters use multiple bytes. The German letter Ä fornisntance is 0xC3 0x48. In addition the Unicode standard has specific rules on sorting and comparing those values and some fancy transformations. (Sorting rules are even language dependent, so the German Ä can be sorted like AE, behind Z or simply as A) Wenn Browsers and JavaScript were created it was decided that a string in JavaScirpt shall be Unicode data. This is logical as websites are full of human readable text and properties of Unicode are good (well, the story is more complicated there, but good enough) This was good for the time where Web was working with simple websites and JavaScript was doing minor text manipulation. However for lower layers of the compitong stack data is just a sequence of bytes. In memory you have bytes. A file is a sequence of bytes. The meaning of those bytes might be Unicode text, might be an image, might even be bianry program code all are just bytes. The difference is only in the one looking at it. Now treating all data as unicode string will do harm, as they have all the assumptions on top where only specific byte sequences are valid and so on. So something else had to be added. And in fact different groups added different things. Before we can explain that, one step more is needed: as said interpretation depends on who looks at the data. So back to our numbers and from decimal and hex to binary. As said 8 bit are a byte. The number 1 in binary with it 8 bits would look like 0b00000001 Here using 0b as prefix, so you interpret it as binary, not hey, not decimal. The value 127 inn inary looks like this: 0b01111111 all bits, but the first set. Now something fancy happens when we set the first bit to 1 as well: 0b11111111 This can either be 255 or -1. Wait what negative!? You will ask: Yes, there eisna problem with these numbers: Our byte has to represent negative numbers as well. And then the first digit tells us whether it's negative or positive. And whenever we look at the byte we have to make a choice how we look at it. Is it a text character? Is it a positive number? A negative number? The byte doesn't know and doesn't care only we when looking at it. Now the Uint8Array enters! By giving a sequence of bytes (some area in memory) to an Uint8Buffer we tell it "look at those bytes and treat tit like a sequence of bytes, where each byte is a 8 bit unsigned number" and by that we can work with those.bytes and each byte will be a number 0 to 256 and whatever we do with the array decides on what it does with those bytes. Maybe it is a pixel in an image, maybe an frequency on an audio file, maybe ... Now another term there eisnthe Buffer. A buffer is just some area in memory. An arrayBuffer is "this is my area of memory, but I haven't yet decided how i will interpret it" I said Buffer, I said complicazednhsorory ... That tis that Node.js developers Hand this issue before ArrayBuffer d Uint8Array was defined, so they created their own thing, which is similar to an Unit8Array (modern versions of Buffer are built on Uint8Array) but don't be confused, buffer is a generic term for some data stored somewhere, which is distinct from Buffer, which is a type in Node.js. Now there ris a bit more. 256 is a bit low formmany purposes. So you can group multiple bytes and make them digits in a larger number. Quite typical are efor 4 byte, which are 32 bit. Thus a Int32Array takes 4 bytes at once from the underlying data (the ArrayBuffer, the buffer, the memory region) and makes it a 32 bit signed number (- 2147483648 to 2147483647) the Uint32Array (0 to 4294967295) and if that isn't enought there are big(u)int64Array, which look at 8 byte at a time, which is also the number of byte/bit a modern CPU can store in it's register, transfer though bus and process the best, hence 64bit architecture. The key thing is: memory (RAM, disk or any other form) in modern computers is just a sequence of bytes and the way you look at it decides on the meaning. The computer doesn't know and you have to tell it. Uint8Array is the typically representation for low level work. ArrayBuffer is when you haven't decided, yet and all else are more special.
2 of 2
1
it's a bit of a Pia esp when different libs want diff types. An ArrayBuffer is raw data. Like a big bag of data. You can't do anything with it - but if you convert it to something that can look inside the bag (Uint8Array), you can read / write it. If you just want to read, then Blob is your guy.
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › API › Blob › arrayBuffer
Blob: arrayBuffer() method - Web APIs - MDN Web Docs
December 2, 2023 - The arrayBuffer() method of the Blob interface returns a Promise that resolves with the contents of the blob as binary data contained in an ArrayBuffer.
Tricentis
tabnine.com › home › products overview
Agentic Quality Engineering Platform - Tricentis
January 31, 2018 - Describe what you want tested and the agent navigates the application, maps the fields, builds the test, and debugs itself when it breaks. Teams report up to 60% productivity gains, and non-experts can finally contribute to automation.
Medium
medium.com › @dev-aditya › buffer-arraybuffer-float64array-in-node-js-ef68c112d905
Buffer, ArrayBuffer, Float64Array in Node.js | by Aditya Yadav | Medium
September 29, 2024 - // Create an ArrayBuffer of 16 bytes const buffer = new ArrayBuffer(16); // Create a Float64Array view const float64View = new Float64Array(buffer); // Assign values float64View[0] = Math.PI; float64View[1] = Math.E; console.log(float64View); ...
Top answer 1 of 2
49
That looks like you've got a string which represents the body of your file.
You just have to make a new buffer with it.
var fileBuffer = Buffer.from(file)
If your encoding is NOT utf8 you can specify an alternate encoding as a second optional argument.
var fileBuffer = Buffer.from(file, 'base64')
If the file is actually on disk, this is even easier, since, by default, the fs.readFile operation returns a buffer.
fs.readFile(file, function(err, buffer){})
If you're in a real old version of node Buffer.from doesn't exist and you have to use a very memory-unsafe new constructor. Please consider upgrading your node instance to support Buffer.from
2 of 2
14
In 2024 this is what I'm doing – which makes typescript happy.
First create an ArrayBuffer from the file, then pass the ArrayBuffer to Buffer.from like so
const arrayBuffer = await file.arrayBuffer()
const buffer = Buffer.from(arrayBuffer)
Stack Overflow
stackoverflow.com › questions › 54821527 › javascript-file-api-to-node-js-how-to-send-arraybuffer-with-data-through-websock
JavaScript file API to node.js how to send ArrayBuffer with data through websocket - Stack Overflow
February 22, 2019 - @dansalias I thinki I ended up opening a new socket for each file uploading, and first sending the string as the name, then listen on the server side for the next message to be an arraybuffer, then link the strink and the arraybuffer, or as other answers said I could have combined the name into the buffer in a custom file format, with a header etc and then read the frist few bytes on the server side to extract the name and get the rest of it by copying the remainder of the arraybuffer
Three.js
discourse.threejs.org › questions
How to create a new file and save it with ArrayBuffer content? - Questions - three.js forum
July 20, 2017 - I have an arraybuffer which i want to save into a new file so i can use them later for other things. how can i store the ArrayBuffer in a txt file and choose the location to save it?
npm
npmjs.com › package › file2arraybuffer
file2arraybuffer - npm
However, keep in mind that the function handles one single file, so by referencing an HTMLInputElement or its FileList attribute will only generate the ArrayBuffer for the el.files[0]. If you are working with multi-file input, you must iterate over the FileList object.
» npm install file2arraybuffer
Published: Jan 06, 2026
Version: 1.3.5
Author: Julio L. Muller
Bun
bun.sh › guides › binary data › arraybuffer to buffer
Convert an ArrayBuffer to a Buffer | Bun Guides
const arrBuffer = new ArrayBuffer(64); const nodeBuffer = Buffer.from(arrBuffer);