javascript - URL.createObjectURL returns a blob with null prepended. Eg : Blob:null/12415-63

Question

blob has null prepended at the start eg : blob:null/72438-4637-23673-34721. But when I use the same as a src to the , it shows up the correct image.

I am using URL.createObjectURL call. I also tried using webkitURL. Both return a blob with null appended at the start. Also the blob value returned by URL and webkitURL are not the same.

Here is the code snippet

        var dataUrl = canvas.toDataURL();

        // The last piece of the data URL after the comma
        var byteString = atob(dataUrl.split(',')[1]);

        // Populate an array buffer
        var arrayBuffer = new ArrayBuffer(byteString.length);
        var uint8Array = new Uint8Array(arrayBuffer);
        for (var i = 0; i < byteString.length; i++) {
            uint8Array[i] = byteString.charCodeAt(i);
        }

        var blob = new Blob([uint8Array], { type: "image/png" });
        var blobVal = URL.createObjectURL(blob);

Here the blobVal has "blob:null/1234-5678-9012- ..."

Answer 1

That's the origin, file system and sandboxed iframes(maybe others) have null as their origin. If you set up a local sever it should say http%3A//localhost, that's http://localhost url encoded

    var arrayBuffer = new ArrayBuffer(100);
var uint8Array = new Uint8Array(arrayBuffer);
for (var i = 0; i < 100; i++) {
uint8Array[i] = i;
}

var blob = new Blob([uint8Array], { type: "image/png" });
var blobVal = URL.createObjectURL(blob);
$('div').html(blobVal);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div></div>