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0.1.3 • Public • Published


file-format converts objects to and from Blobs, Base64, or ArrayBuffers with the freedom to shape things as a JSON object. This is useful for packing complex types of data into a single file for your applications file format, or bundling resource fetched over a network.

This library is primarily designed for Browser / Electron usage, though Node usage is possible for Node versions higher than 15.7.

Blob support is poor/non-existent in older version of Node (< v15.7) - see the Blob Node compatibility info. Use a polyfill like cross-blob if required.


Install as dependency through npm.

npm install file-format

Defining your format

To define a format just create either an object or an array with keys/values/items of these supported types:

  • string
  • number
  • boolean
  • null
  • Blob
  • ArrayBuffer

Also supports arbitrary Arrays and Object combinations of these types.

You're free to structure things as required, these types should provide all the flexibility to capture a self-contained file. For example, you can store images as blobs and any metadata required as a single file.

Here's an example of an arbitrary file format:

// define an object with any sub structures based on the supported types...

const myFileFormat = {
  aNullProp: null,
  aStringProp: "x",
  aNumberProp: 123,
  anArrayProp: [null, "bar", 123, { x: 1 }],
  aBoolean: true,
  theOtherBoolean: false,
  aComplexArray: ["a", "b", { c: false, d: [1, 2, [3, null]] }],
  aBlobProp: blob,
  someObjectProp: {
    subProp1: {
      subProp2: true,
  anArrayBufferProp: arrayBuffer,
  anotherNumber: 1000.55,

// or define it as an array
const myFileFormat = [
  // ...same supported types as above, with any nesting or sub structures required

Writing to a Blob

To create a Blob, Base64, or ArrayBuffer from an object use the DataWriter and call toBlob(), toArrayBuffer() or toBase64() respectively.

import { DataWriter } from "file-format";

const writer = new DataWriter();

writer.serialise(myFileFormat).then(() => {
  // create a Blob...
  const blob = writer.toBlob();
  // or an ArrayBuffer...
  const arrayBuffer = writer.toArrayBuffer();
  // or a Base64 String...
  const base64 = writer.toBase64();

Reading from a Blob

To read a Blob or Base64 String use the DataReader. You can pass in a Blob or base64 string.

import { DataReader } from "file-format";

const reader = new DataReader();

reader.deserialise(blobOrBase64String).then((myFileFormat) => {
  // myFileFormat is an object just as you originally saved it...

NOTE: The blob must have been created by a DataWriter otherwise unexpected errors will occur during read.


Please report any issues here.



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npm i file-format

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  • dragonworx