code: function _checkBlobSupportWithoutCaching(idb) {
  	        return new Promise(function (resolve, reject) {
  	            var blob = _createBlob([''], { type: 'image/png' });
  	            var txn = idb.transaction([DETECT_BLOB_SUPPORT_STORE], 'readwrite');
  	            txn.objectStore(DETECT_BLOB_SUPPORT_STORE).put(blob, 'key');
  	            txn.oncomplete = function () {
  	                // have to do it in a separate transaction, else the correct
  	                // content type is always returned
  	                var blobTxn = idb.transaction([DETECT_BLOB_SUPPORT_STORE], 'readwrite');
  	                var getBlobReq = blobTxn.objectStore(DETECT_BLOB_SUPPORT_STORE).get('key');
  	                getBlobReq.onerror = reject;
  	                getBlobReq.onsuccess = function (e) {
  
  	                    var storedBlob = e.target.result;
  	                    var url = URL.createObjectURL(storedBlob);
  
  	                    _blobAjax(url).then(function (res) {
  	                        resolve(!!(res && res.type === 'image/png'));
  	                    }, function () {
  	                        resolve(false);
  	                    }).then(function () {
  	                        URL.revokeObjectURL(url);
  	                    });
  	                };
  	            };
  	        })['catch'](function () {
  	            return false; // error, so assume unsupported
  	        });
  	    }
docs: Detect blob support. Chrome didn't support it until version 38. In version 37 they had a broken version where PNGs (and possibly other binary types) aren't stored correctly, because when you fetch them, the content type is always null.  Furthermore, they have some outstanding bugs where blobs occasionally are read by FileReader as null, or by ajax as 404s.  Sadly we use the 404 bug to detect the FileReader bug, so if they get fixed independently and released in different versions of Chrome, then the bug could come back. So it's worthwhile to watch these issues: 404 bug: https://code.google.com/p/chromium/issues/detail?id=447916 FileReader bug: https://code.google.com/p/chromium/issues/detail?id=447836