Cross-browser utils for working with binary Blobs
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Latest commit fbe16e8 May 22, 2018

README.md

blob-util Build Status TypeScript

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

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.

Kirby

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


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