Convert Blob to binary string synchronously

filereader, javascript, synchronous

Solution

Here is a hacky-way to get you synchronously from a blob to its bytes. I'm not sure how well this works for any binary data.

function blobToUint8Array(b) {
    var uri = URL.createObjectURL(b),
        xhr = new XMLHttpRequest(),
        i,
        ui8;
    
    xhr.open('GET', uri, false);
    xhr.send();
    
    URL.revokeObjectURL(uri);
    
    ui8 = new Uint8Array(xhr.response.length);
    
    for (i = 0; i < xhr.response.length; ++i) {
        ui8[i] = xhr.response.charCodeAt(i);
    }
    
    return ui8;
}

var b = new Blob(['abc'], {type: 'application/octet-stream'});
blobToUint8Array(b); // [97, 98, 99]

You should consider keeping it async but making it two-stage, though, as you may end up locking up the browser.

Additionally, you can skip Blobs entirely by including a binary-safe Base64 decoder, and you probably don't need to go via Base64 AND Blob, just one of them.

Problem

I'm trying to put image in clipboard when user copies canvas selection: So I thought the right way would be to convert canvas tu dataURL, dataURL to blob and blob to binary string. Theoretically it should be possible to skip the blob, but I don't know why. So this is what I did: ``` function copy(event) { console.log("copy"); console.log(event); //Get DataTransfer object var items = (event.clipboardData || event.originalEvent.clipboardData); //Canvas to blob var blob = Blob.fromDataURL(_this.editor.selection.getSelectedImage().toDataURL("image/png")); //File reader to convert blob to binary string var reader = new FileReader(); //File reader is for some reason asynchronous reader.onloadend = function () { items.setData(reader.result, "image/png"); } //This starts the conversion reader.readAsBinaryString(blob); //Prevent default copy operation event.preventDefault(); event.cancelBubble = true; return false; } div.addEventListener('copy', copy); ``` But when the `DataTransfer` object is used out of the `paste` event thread the `setData` has no longer any chance to take effect. How can I do the conversion in the same function thread?

Original source