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The onblocked event handler of the IDBOpenDBRequest interface is the event handler for the blocked event. This event is triggered when the upgradeneeded should be triggered because of a version change but the database is still in use (that is, not closed) somewhere, even after the versionchange event was sent.

Note: This feature is available in Web Workers.


IDBOpenDBRequest.onblocked = function(event) { ... };


var db;

// Let us open our database
var request = indexedDB.open("toDoList", 4);

// these two event handlers act on the database being opened
// successfully, or not
request.onerror = function(event) {
  note.innerHTML += '<li>Error loading database.</li>';

request.onsuccess = function(event) {
  note.innerHTML += '<li>Database initialised.</li>';
  // store the result of opening the database in the db variable.
  // This is used a lot below
  db = request.result;
  // Run the displayData() function to populate the task list with
  // all the to-do list data already in the IDB

// This event handles the event whereby a new version of the
// database needs to be created. Either one has not been created
// before, or a new version number has been submitted via the
// window.indexedDB.open line above
//it is only implemented in recent browsers
request.onupgradeneeded = function(event) {
  var db = event.target.result;
  db.onerror = function(event) {
    note.innerHTML += '<li>Error loading database.</li>';

  // Create an objectStore for this database   
  var objectStore = db.createObjectStore("toDoList", { keyPath: "taskTitle" });


request.onblocked = function() {
  console.log("Your database version can't be upgraded because the app is open somewhere else.");


Specification Status Comment
Indexed Database API
The definition of 'onblocked' in that specification.
Indexed Database API 2.0
The definition of 'onblocked' in that specification.

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support


23 — 57 webkit



10 — 16 moz

FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support


23 — 57 webkit


23 — 57 webkit

Yes22228 ?

1. partial

See also

Document Tags and Contributors

 Contributors to this page: fscholz, jpmedley, libbymc, chrisdavidmills, teoli, eharris, eicto
 Last updated by: fscholz,