HTML5 / Javascript - DataURL to Blob & Blob to DataURL

Question

I have a DataURL from a canvas that shows my webcam. I turn this dataURL into a blob using Matt's answer from here: How to convert dataURL to file object in javascript?

How do I convert this blob back into the same DataURL? I've spent a day researching this and I'm astouned this isn't documented better, unless I'm blind.

EDIT: There is

var urlCreator = window.URL || window.webkitURL; 
var imageUrl = urlCreator.createObjectURL(blob); 

but it only returns a really short URL that seems to point at a local file, but I need to send the webcam data over a network.

Answer 1

Use my code to convert between dataURL and blob object in javascript. (better than the code in your link.)

//**dataURL to blob**
function dataURLtoBlob(dataurl) {
    var arr = dataurl.split(','), mime = arr[0].match(/:(.*?);/)[1],
        bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
    while(n--){
        u8arr[n] = bstr.charCodeAt(n);
    }
    return new Blob([u8arr], {type:mime});
}

//**blob to dataURL**
function blobToDataURL(blob, callback) {
    var a = new FileReader();
    a.onload = function(e) {callback(e.target.result);}
    a.readAsDataURL(blob);
}

//test:
var blob = dataURLtoBlob('data:text/plain;base64,YWFhYWFhYQ==');
blobToDataURL(blob, function(dataurl){
    console.log(dataurl);
});