blob-util

blob-util is a Blob library for busy people.

It offers a small set of cross-browser utilities for translating Blobs to and from different formats:

• <img/> tags
• base 64 strings
• binary strings
• ArrayBuffers
• data URLs
• canvas

It's also a good pairing with the attachment API in PouchDB.

Note: this is a browser library. For Node.js, see Buffers.

Topics:

• Install
• Browser support
• Tutorial
• Playground
• API

Install

Via npm:

npm install blob-util

ES modules are supported:

import { canvasToBlob } from 'blob-util'
canvasToBlob(canvas, 'image/png').then(/* ... */)

Or as a script tag:

<script src="https://unpkg.com/blob-util/dist/blob-util.min.js"></script>

Then it's available as a global blobUtil object:

blobUtil.canvasToBlob(canvas, 'image/png').then(/* ... */)

Browser support

As of v2.0.0, a built-in Promise polyfill is no longer provided. Assuming you provide a Promise polyfill, the supported browsers are:

• Firefox
• Chrome
• Edge
• IE 10+
• Safari 6+
• iOS 6+
• Android 4+
• Any browser with either Blob or the older BlobBuilder; see caniuse for details.

Tutorial

Blobs (binary large objects) are the modern way of working with binary data in the browser. The browser support is very good.

Once you have a Blob, you can make it available offline by storing it in IndexedDB, PouchDB, LocalForage, or other in-browser databases. So it's the perfect format for working with offline images, sound, and video.

A File is also a Blob. So if you have an <input type="file"> in your page, you can let your users upload any file and then work with it as a Blob.

Example

Here's Kirby. He's a famous little Blob.

So let's fulfill his destiny, and convert him to a real Blob object.

var img = document.getElementById('kirby');

blobUtil.imgSrcToBlob(img.src).then(function (blob) {
  // ladies and gents, we have a blob
}).catch(function (err) {
  // image failed to load
});

(Don't worry, this won't download the image twice, because browsers are smart.)

Now that we have a Blob, we can convert it to a URL and use that as the source for another <img/> tag:

var blobURL = blobUtil.createObjectURL(blob);

var newImg = document.createElement('img');
newImg.src = blobURL;

document.body.appendChild(newImg);

So now we have two Kirbys - one with a normal URL, and the other with a blob URL. You can try this out yourself in the blob-util playground. Super fun!

API

Index

Functions

• arrayBufferToBinaryString
• arrayBufferToBlob
• base64StringToBlob
• binaryStringToArrayBuffer
• binaryStringToBlob
• blobToArrayBuffer
• blobToBase64String
• blobToBinaryString
• blobToDataURL
• canvasToBlob
• createBlob
• createObjectURL
• dataURLToBlob
• imgSrcToBlob
• imgSrcToDataURL
• revokeObjectURL

---

Functions

arrayBufferToBinaryString

▸ arrayBufferToBinaryString(buffer: ArrayBuffer): string

Convert an ArrayBuffer to a binary string.

Example:

var myString = blobUtil.arrayBufferToBinaryString(arrayBuff)

Parameters:

Param	Type	Description
buffer	ArrayBuffer	array buffer

Returns: string binary string

---

arrayBufferToBlob

▸ arrayBufferToBlob(buffer: ArrayBuffer, type?: string): Blob

Convert an ArrayBuffer to a Blob.

Example:

var blob = blobUtil.arrayBufferToBlob(arrayBuff, 'audio/mpeg');

Parameters:

Param	Type	Description
buffer	ArrayBuffer	-
Optional type	string	the content type (optional)

Returns: Blob Blob

---

base64StringToBlob

▸ base64StringToBlob(base64: string, type?: string): Blob

Convert a base64-encoded string to a Blob.

Example:

var blob = blobUtil.base64StringToBlob(base64String);

Parameters:

Param	Type	Description
base64	string	base64-encoded string
Optional type	string	the content type (optional)

Returns: Blob Blob

---

binaryStringToArrayBuffer

▸ binaryStringToArrayBuffer(binary: string): ArrayBuffer

Convert a binary string to an ArrayBuffer.

var myBuffer = blobUtil.binaryStringToArrayBuffer(binaryString)

Parameters:

Param	Type	Description
binary	string	binary string

Returns: ArrayBuffer array buffer

---

binaryStringToBlob

▸ binaryStringToBlob(binary: string, type?: string): Blob

Convert a binary string to a Blob.

Example:

var blob = blobUtil.binaryStringToBlob(binaryString);

Parameters:

Param	Type	Description
binary	string	binary string
Optional type	string	the content type (optional)

Returns: Blob Blob

---

blobToArrayBuffer

▸ blobToArrayBuffer(blob: Blob): Promise<ArrayBuffer>

Convert a Blob to an ArrayBuffer.

Example:

blobUtil.blobToArrayBuffer(blob).then(function (arrayBuff) {
  // success
}).catch(function (err) {
  // error
});

Parameters:

Param	Type	Description
blob	Blob	-

Returns: Promise<ArrayBuffer> Promise that resolves with the ArrayBuffer

---

blobToBase64String

▸ blobToBase64String(blob: Blob): Promise<string>

Convert a Blob to a binary string.

Example:

blobUtil.blobToBase64String(blob).then(function (base64String) {
  // success
}).catch(function (err) {
  // error
});

Parameters:

Param	Type	Description
blob	Blob	-

Returns: Promise<string> Promise that resolves with the binary string

---

blobToBinaryString

▸ blobToBinaryString(blob: Blob): Promise<string>

Convert a Blob to a binary string.

Example:

blobUtil.blobToBinaryString(blob).then(function (binaryString) {
  // success
}).catch(function (err) {
  // error
});

Parameters:

Param	Type	Description
blob	Blob	-

Returns: Promise<string> Promise that resolves with the binary string

---

blobToDataURL

▸ blobToDataURL(blob: Blob): Promise<string>

Convert a Blob to a data URL string (e.g. 'data:image/png;base64,iVBORw0KG...').

Example:

var dataURL = blobUtil.blobToDataURL(blob);

Parameters:

Param	Type	Description
blob	Blob	-

Returns: Promise<string> Promise that resolves with the data URL string

---

canvasToBlob

▸ canvasToBlob(canvas: HTMLCanvasElement, type?: string, quality?: number): Promise<Blob>

Convert a canvas to a Blob.

Examples:

blobUtil.canvasToBlob(canvas).then(function (blob) {
  // success
}).catch(function (err) {
  // error
});

Most browsers support converting a canvas to both 'image/png' and 'image/jpeg'. You may also want to try 'image/webp', which will work in some browsers like Chrome (and in other browsers, will just fall back to 'image/png'):

blobUtil.canvasToBlob(canvas, 'image/webp').then(function (blob) {
  // success
}).catch(function (err) {
  // error
});

Parameters:

Param	Type	Description
canvas	HTMLCanvasElement	HTMLCanvasElement
Optional type	string	the content type (optional, defaults to 'image/png')
Optional quality	number	a number between 0 and 1 indicating image quality if the requested type is 'image/jpeg' or 'image/webp'

Returns: Promise<Blob> Promise that resolves with the Blob

---

createBlob

▸ createBlob(parts: Array<any>, properties?: * BlobPropertyBag | string*): Blob

Shim for new Blob() to support older browsers that use the deprecated BlobBuilder API.

Example:

var myBlob = blobUtil.createBlob(['hello world'], {type: 'text/plain'});

Parameters:

Param	Type	Description
parts	Array<any>	content of the Blob
Optional properties	BlobPropertyBag | string	usually {type: myContentType}, you can also pass a string for the content type

Returns: Blob Blob

---

createObjectURL

▸ createObjectURL(blob: Blob): string

Shim for URL.createObjectURL() to support browsers that only have the prefixed webkitURL (e.g. Android <4.4).

Example:

var myUrl = blobUtil.createObjectURL(blob);

Parameters:

Param	Type	Description
blob	Blob	-

Returns: string url

---

dataURLToBlob

▸ dataURLToBlob(dataURL: string): Blob

Convert a data URL string (e.g. 'data:image/png;base64,iVBORw0KG...') to a Blob.

Example:

var blob = blobUtil.dataURLToBlob(dataURL);

Parameters:

Param	Type	Description
dataURL	string	dataURL-encoded string

Returns: Blob Blob

---

imgSrcToBlob

▸ imgSrcToBlob(src: string, type?: string, crossOrigin?: string, quality?: number): Promise<Blob>

Convert an image's src URL to a Blob by loading the image and painting it to a canvas.

Note: this will coerce the image to the desired content type, and it will only paint the first frame of an animated GIF.

Examples:

blobUtil.imgSrcToBlob('http://mysite.com/img.png').then(function (blob) {
  // success
}).catch(function (err) {
  // error
});

blobUtil.imgSrcToBlob('http://some-other-site.com/img.jpg', 'image/jpeg',
                         'Anonymous', 1.0).then(function (blob) {
  // success
}).catch(function (err) {
  // error
});

Parameters:

Param	Type	Description
src	string	image src
Optional type	string	the content type (optional, defaults to 'image/png')
Optional crossOrigin	string	for CORS-enabled images, set this to 'Anonymous' to avoid "tainted canvas" errors
Optional quality	number	a number between 0 and 1 indicating image quality if the requested type is 'image/jpeg' or 'image/webp'

Returns: Promise<Blob> Promise that resolves with the Blob

---

imgSrcToDataURL

▸ imgSrcToDataURL(src: string, type?: string, crossOrigin?: string, quality?: number): Promise<string>

Convert an image's src URL to a data URL by loading the image and painting it to a canvas.

Note: this will coerce the image to the desired content type, and it will only paint the first frame of an animated GIF.

Examples:

blobUtil.imgSrcToDataURL('http://mysite.com/img.png').then(function (dataURL) {
  // success
}).catch(function (err) {
  // error
});

blobUtil.imgSrcToDataURL('http://some-other-site.com/img.jpg', 'image/jpeg',
                         'Anonymous', 1.0).then(function (dataURL) {
  // success
}).catch(function (err) {
  // error
});

Parameters:

Param	Type	Description
src	string	image src
Optional type	string	the content type (optional, defaults to 'image/png')
Optional crossOrigin	string	for CORS-enabled images, set this to 'Anonymous' to avoid "tainted canvas" errors
Optional quality	number	a number between 0 and 1 indicating image quality if the requested type is 'image/jpeg' or 'image/webp'

Returns: Promise<string> Promise that resolves with the data URL string

---

revokeObjectURL

▸ revokeObjectURL(url: string): void

Shim for URL.revokeObjectURL() to support browsers that only have the prefixed webkitURL (e.g. Android <4.4).

Example:

blobUtil.revokeObjectURL(myUrl);

Parameters:

Param	Type	Description
url	string

Returns: void

---

Credits

Thanks to the rest of the PouchDB team for figuring most of this crazy stuff out.

Building the library

npm install
npm run build

Testing the library

npm install

Then to test in the browser using Saucelabs:

npm test

Or to test locally in your browser of choice:

npm run test-local

To build the API docs and insert them in the README:

npm run doc