added supporting method for converting data URL to Blob

vfs.js

@@ -179,6 +179,30 @@ let VFS = function() {
         return dataUrl;
     };
 
+    this.dataURLToBlob = function(dataURL) {
+        // convert base64 to raw binary data held in a string
+        // doesn't handle URLEncoded DataURIs - see SO answer #6850276 for code that does this
+        var byteString = atob(dataURL.split(',')[1]);
+
+        // separate out the mime component
+        var mimeString = dataURL.split(',')[0].split(':')[1].split(';')[0]
+
+        // write the bytes of the string to an ArrayBuffer
+        var ab = new ArrayBuffer(byteString.length);
+
+        // create a view into the buffer
+        var ia = new Uint8Array(ab);
+
+        // set the bytes of the buffer to the correct values
+        for (var i = 0; i < byteString.length; i++) {
+            ia[i] = byteString.charCodeAt(i);
+        }
+
+        // write the ArrayBuffer to a blob, and you're done
+        var blob = new Blob([ab], {type: mimeString});
+        return blob;
+    };
+
     function getTypeFromName(filename) {
         var parts = filename.split(".");
         if (parts.length < 2) { return null; }